Maintaining knives with my few tools

Diamond abrasives eat kitchen knives.  You're better staying away from the diamond surfaces if possible.  Especially the DMT mini. 

Small stones are very difficult to use with big knives.  You don't have enough length or width to develop a consistent angle or even bevel. 

Chromium dioxide is 0.5u (1/2 micron) screen which is a very fine grit indeed.  Fine enough to polish a cut-throat razor, and too fine to do any sharpening.  Considering how coarse your other surfaces are, you can't do more than shine up the scratches.  You certainly can't buff them out.

Yes, you can true your edges by stropping on a board in lieu of using a steel.  It's not as fast or as convenient, but will do a perfectly fine job as long as you hold your angles steady.  Just avoid pulling a burr when you strop, or be prepared to deburr.  Good hones aren't that expensive ($30ish) and some of your knives -- the Nogent especially -- profit mightily from frequent steeling. 

Overall, your sharpening kit isn't doing you or your knives much of a service.  You lack the basics, which are a good coarse stone for profile/repair, a good medium-coarse to pull the first burr, and a good medium-fine to finish sharpening and get rid of the scratch left by the medium-coarse stone. 

Ordinarily I'd recommend a Norton combination India stone to take the first two slots and a black Arkansas as an economical and complete (if abbreviated) kit -- or even an 8" tri-hone.  You want something fairly fine as your last stone if only for the Nogent and the VG-10 -- but oilstones are awfully slow for that VG-10.  Unfortunately because of the exchange rate, even inexpensive waterstones like Kings aren't inexpensive any more.

Getting you kitted up and staying within your budget isn't going to be easy.  Maybe something like a pink brick, a King 1K and some 2u stropping compound.  Or maybe a Hall's tri-hone with a medium manmade, a soft Ark and a black Ark. 

BDL

Hoi,

The biggest challenges here are your limited budget and your motley set of knives.  Some of them are made from soft, tough steels (like most European made stainless) which sharpens better on American and European type stones.  But your VG-10 would sharpen so slowly on those it would not only be frustrating but difficult to maintain your angles.  Fortunately, your new (to you) Nogent will sharpen equally well on water and oil stones. 

By the way, if you purchased it in Europe, may I ask from whom you bought it?  

Getting back to sharpening:  In addition to all the other plusses and minusses, water stones need their own preparation and maintenance, i.e., soaking, flattening and lapping.  Flattening and lapping requires twice as much frequency with combi-stones, because they only have one surface for each grit. 

All things considered, the 800/5000 covers a lot of territory and might be your best choice.  You can add a 400 (or so) when you need it. 

Another alternative is an 8" Norton combination India stone which would translate to around 300/750 in Japanese grits measurements (JIS).  The two big problems with the India are (a) finding one in Europe for a reasonable price; and (b) while it will work, it's a not a great choice for VG-10.  Everything considered, waterstones are probably the best choice.

For whatever reason, Naniwa seems to come up a lot in conversations with Europeans asking for advice about stones.  They're fine, resin-binder stones, but they're expensive.  You should consider natural clay-binder King, Sun Tiger and Suehiro as well.  However, if you can work with a slightly smaller stone, the "small" Naniwa 15mm SS series pre-mounted on plastic stands are relatively inexpensive -- perhaps sufficiently so that you can purchase three stones. 

Returning to King stones, they make a 1000/6000 that's quite good -- as combi stones go.  A couple of the Kings, 1200 and 6000, are particularly excellent single-grit stones

You could get away with two stones:  A coarse (400 or 500 -- for profile/repair), and a medium-coarse (for "pulling a wire," aka "raising a burr," aka sharpnening.  Then finishing with a loaded strop using 2u -- or thereabouts -- stropping compund. 

Just looking at the German, Dieter Schmid website, as being representative of the sort of selection and prices you'd see in the Netherlands I think your best bet there would either to go with three smaller SS (€ 40 for the set), or combining the "small" coarse Naniwa (€ 12) with the large, King 1000/6000 combination stone (€ 43). 

The small Naniwas at Schmid are 175mm x 55mm x 15mm, as small is as useful for kitchen knives.  15mm is on the borderline of actually needing a separate sharpening stand (as opposed to using a piece of non-skid drawer liner, for instance).  Naniwa also makes a longer, wider, thinner, value-priced Super Stone, which I believe is a more useful size.  Whether or not you can find them in Holland, who knows? 

By the way, many experienced sharpeners prefer to use their own stands rather than buying pre-attached stones.  Although attached stands have the drawvack of limiting you to one surface at a time, they provide some very useful benefits as well.  My advice is not to let it scare you away from the 10mm stones (if you can find and afford them).

If you're not a consistently good sharpener yet, you might want to consider 1000 and 3000 as your two finer surfaces.  If you can't consistently sharpen with a 3000 (mostly a matter of holding a constant, steady angle), you'll find higher grits counter-productive and run the risk of creating serious problems with a coarse stone.

The best way to develop consistency is to learn to draw a burr and then deburr at the 1000, before moving one  to the 3000 grit level.  Learning on a 3000 goes faster and is less frustrating than learning on a 5000 or 6000; but once you've learned to sharpen consistently on a 3000, you can work with anything.  On the other hand, the difference in the learning curves is not huge.  Many, many people have learned their skills on a King 1000/6000.   

Finally, pardon me if this seems somewhat disconnected. 

Hope this helps,

BDL

I would also be very interested to hear other people's opinions.

I'm contemplating the 1000/3000 Naniwa work stone or the 800 or 1000 superstone combined with the 3000 superstone.

You have to view stones in context -- and nothing is perfect.  The 3K SS is an excellent stone.  It's reasonably fast on any type of steel, is incredibly "communicative," doesn't require extensive soaking, flattens so easily, and the results are extremely visible.  But the stone needs frequent flattening, and needs very thorough drying.  It's susceptible to losing the corners if the edges aren't properly beveled, and also more susceptible to gouging than most stones at the grit level.

All that feedback -- including the extra care it takes to hold an angle so as not to cut into the stone -- is excellent for a beginning sharpener.  All the way through the range, an SS will tell you very quickly if you're sharpening wrong.  The pre-mounted, 1cm (thin) stones are especially good "learners." 

While the SS is a very good 3K for any sharpener regardless of skill level, depending on the sharpener there are probably better at or around the grit level.  For that matter, 3K is not necessarily the best medium-fine grit level for any given set. 

I actually do use a 3K in mine, a Chocera (almost twice as much at retail as an SS) which I lucked into at a HUGE discount.  As good as the Chocera is, I wouldn't miss it at all if it were replaced by an SS 3K, an Arashiyama, a Suehiro Rika, or any of several other stones tomorrow.  What's important to me from the medium fine stone in my kit is that it polish out the 1K scratches from the previous stone; draws a suitably fine burr; and does both things quickly.  In other words, that it does a medium-fine stone's job and does it well.  I don't care much about feedback or about relative ease of use one way or the other -- but that's me.  While you're learning, you might as well make learning itself as easy as possible.

Regarding Loremipsum's questions specifically:  I think 1K/6K and 800/5K are big jumps and that 5K and 6K can be somewhat frustrating for a beginner.  You'll find the 1K/3K easier to learn on.  IIRC, at this stage of the game, neither of you has a knife that demands more polish, so that would be my first recommendation.  Still, I know plenty of people who learned on King 1K/6Ks and plenty (some of them the same people), including more than a few pros) who use that stone.  The 800/5K is also very good, but it's uncommon in the US. 

Hope this helps,

BDL