We're trying to kill too many grits with one $50 bill and it's getting very confusing.
One thing it's important to know is which Norton Combi stone you're using. If it's either 8" or the 11" coarse/fine India, that's "fine for now" when it comes to repair/profiling and raising a burr.
If it's one of the shorter India combis, or a Norton Crystolon, you should probably either replace it with a larger coarse/fine India or just go ahead and buy a decent 1000# stone.
Assuming it's an 8" or better -- it doesn't really make a lot of sense to buy a 1000# (JIS) waterstone, since the Norton is the functional equivalent of around 750# JIS. Given your budget, I don't think it makes sense to blow the whole thing on a Chosera 1000#, no matter how good a stone it is.
Choseras are great stones -- maybe even the "best," at any given grit level -- but they're very expensive compared to stones that will do as good a job and are fast, but not quite as fast; and very expensive compared to stones that will do almost as good a job and are still fast.
Given your particular knife kit and budget, a Chosera is just way too much stone -- for now. Later is another matter.
Also, there's a limit to how good an edge you're going to get with any 1000# stone. That edge is better than a fine India's, but a 1000# is a grit level for pulling a wire but not so much for chasing it and certainly not for polishing.
It's probably not worthwhile going beyond 5K or 6K on your current knife -- so no need to look at 8K stones. But you might as well hear the good news now -- if you can raise a burr and deburr it consistently, you can learn to polish at any grit level without too much more effort. It's simply a matter of doing what you're already doing with a lot of consistency, and possibly a little more "touch."
Getting back to your immediate situation, jumping from a fine India to 5000# or 6000# stone is doable, but it's a lot of jump especially for someone who hasn't polished before.
Your ideal stone is probably something like a Suehiro Rika -- a stone with which I have NO personal experiences. It's nominally 5K, but it's supposedly very fast for the grit level -- which means not so much of a jump from the fine India. On the negative side, it doesn't seem to polish quite as well as other high end, more expensive 5Ks. Still, if and when you do move on to hard-alloy Japanese cutlery it's supposedly a good transition to a true, high grit polishing stone.
You can find the Rika here: Hida Tool & Hardware Co., Inc.
, and Hida is a great place. Another stone Hida carries which might work well for you is the "synthetic blue stone." It's what's called an "aoto," and is meant to be used as the medium transitional stone before moving on to a polishing stone.
The aoto and the rika share some characteristics. They both mimic natural stones in that they combine a mix of grit sizes; they are both very soft stones; consequently, they make a lot of mud (which is going to be new to you); dish like crazy, and need a lot of flattening.
Perhaps a better solution than either of those mud bound stones, and still semi-reasonably priced, would be a 5000# Naniwa Super Stone from Sharpening Supplies. I especially like these stones for most beginners -- but actually not so much for you.
Worth considering is a Norton 4000# stand alone. Nortons are also mud-bound stones but they're extremely consistent and harder than most similar stones -- especially Kings. The stone is within your budget, easily "reachable" from your fine India, and a good choice to learn about waterstone maintenance.
The waterstone I'd most like to see you get is a Takenoko/Arashiyama (same stone, different names) -- which is sold as all sorts of different grits, but is actually 6000#. But, it's expensive (not as much as a Chosera, but still expensive), and even though it's got a lot of reach it's probably too much to ask someone who hasn't done much polishing to make the jump to an Arashiyama from a fine India.
Alternatively, if you're not going to move on to Japanese knives but stay with the Europeans, you could go pretty handily from the Norton fine India to a Hall's surgical black Arkansas. A Hall's black Ark (or Hall's or Norton translucent Ark) is as good an edge as your knife will take -- maybe better. In my personal set, I interpose a soft Ark after the fine India and before the black Ark. That combination of those two India and two Arkansas stones is a very fine kit indeed -- as long as you're not dealing with very hard steel.
One reason I like (and own) the kit is its evocative association with the way things used to be done. That might not cut much weight with you, and you may not want to invest in Arkansas stones for what will end up being a kit that has to be completely replaced when you start buying Japanese knives. Tough call.
When it comes to Arkansas stones, Hall's is both the value and quality stand out. On the other hand, Norton has nicer boxes.
It's worth repeating that you've got a couple of advantages going in. First, you already know how to sharpen. That's a biggie. And, don't be modest, there are few amongst us who couldn't benefit from more practice. Second, you've learned to sharpen on hard stones. When and if you do move on to waterstones you won't need soft stones as a training transition on your way to better stones held together with resin binders. That's why I'm not just pointing you to the Naniwa Super Stones.