I'm late to this party, but I want to re-emphasize what gNnairdA just said.
If you're looking to recreate udon soup noodles the way you get them in Japan, there is one ingredient that matters more than any other: dashi. If you use chicken broth, beef broth, clam broth, who knows what, it will not taste the same at all.
Furthermore, classic udon the usual way -- kake udon -- is very, very simple. Its depth of flavor does not come from strong ingredients as such. Certainly no hot oil and all that.
Ideally, you should also use fresh noodles. Udon are very plain, pale wheat noodles made without egg. The fresh ones ought to be packed in a cornstarch/low-gluten flour mix, but I've rarely seen them that way in the US. Instead they're packed in oil. So the first thing to do is to rinse your noodles well in cool tap water, then toss in a sieve until nearly dry, and only then boil them.
Now here's what you do.
Start with a biggish piece of the best-quality kombu you can find, which may be mediocre indeed, but them's the breaks. Dab it lightly with a damp cloth to remove any actual dust, but anything you can really see on there isn't dust and shouldn't be removed. Drop the kombu into cold water. (You need a lot more kombu than you think: for 1 liter of water, try a square a good 3" on a side, minimum.) Raise the temperature slowly and hold it at 140 degrees F for as long as you can -- an induction burner works perfectly for this. In a perfect world, hold it that way for an hour. Don't let the temperature come over 165F or it will become slimy and have a mediocre flavor. Remove the kombu with chopsticks. Raise the heat to just under a boil -- about 185F -- and pour in a pile of best-quality bonito flakes. Again, you need a lot more than you think: about 25g for a liter, and as much as 50g, which is probably going to be about half of one of the big bags. Immediately shut off the heat. Wait 1 minute, no more, then immediately strain fine and do NOT press on the bonito flakes. This "first dashi," if allowed to cool to room temperature, will last, covered in the refrigerator, about 48 hours at the outside. It's best to use it the same day.
Mix up a seasoning mixture. For 1 liter of dashi, you want 3 Tb sake, 1 1/2 Tb light soy sauce, 1 tsp salt, and 2 Tb mirin. The sake should be drinkable as wine -- don't use "cooking sake" which is to sake what "cooking wine" from the grocery store is to drinkable wine. Your light soy sauce should be Japanese-style: Chinese-style soy sauces have a quite different taste and will tend to overpower your dish here. Good Japanese regular soy sauce -- even Kikkoman, which makes a nice product -- can be used effectively, but do not use dark soy sauce (often labeled tamari). The mirin should be drinkable as well, not that you'd really want to. Check the ingredients. If you see any kind of sweetener -- usually corn syrup -- this is not real mirin. It can pass, but you would be better off buying a bottle of decent sweetish sake and shaking it up with a little sugar or simple syrup; keep in the fridge for cooking use. It should be distinctly sweet, but not sickly. This should make just about exactly 100ml of seasoning.
Once your dashi is ready, keep it at a bare simmer, and meanwhile bring a very large pot of water to a rolling boil. There is some disagreement about whether the water should be salted; my sense is that most Japanese noodle cooks do not salt the water for udon, but you can suit yourself so long as you don't salt it strongly. Ideally, get out one basket strainer per serving, and make sure that the water level is such that the strainers will hang on the rim of the pot with the strainer rim just above the water level. Put one serving of noodles, rinsed and gently coiled, into each basket strainer, and lower them into the water, hanging the strainers on the rim. Ideally you should do this at 15-20 second intervals, so they all come out cooked the same amount of time. When one is done -- which will be very fast, rarely as much as 2 minutes, but it depends on your noodles -- immediately throw it into a strainer (preferably a woven bamboo one), run cold water over it, and with your asbestos hands whisk the noodles around in the strainer with the water running. After 10 seconds, when they're just barely cooled, toss them into a serving bowl and grab the next portion. (Now you see why you want the interval between portions!)
For each serving, you will need about 1/2 liter of dashi and 1/2 of the above-listed seasoning liquid, i.e. 500cc dashi and 50cc seasoning. Pour the seasoning and the hot dashi over the noodles simultaneously.
Garnishes for udon are many and varied. In my experience there are three near-necessities. You need finely-sliced scallion rings, two or three 1-2mm thick slices of kamaboko fish cake (comes in white and pink, buy it at the Asian market, where it comes formed and steamed on a piece of board -- just slice on the board and then under the slices), and usually simmered agedofu (fried tofu). It's perfectly fine without the tofu, but without scallion and kamaboko it's usually going to have something else more unusual.
To make the tofu, buy medium-sized (maybe 2" on a side) square slices of deep-fried tofu at the Asian market, where they come in packs in the same place you get the fresh tofu. Pour boiling water over them to remove the excess oil. Cut them diagonally into triangles. Place them in a saute pan with 200cc dashi and a generous Tb of good sake. Simmer for a minute or two. Add 1 tsp mirin and 2 tsp light soy sauce, swirl to mix, and then cover it with a lid one size smaller than the pan, holding everything under the liquid. Cook on low heat until the liquid is almost completely gone. Put two triangles on each bowl of udon.
I would recommend putting the tofu and the scallions on the noodles, then adding the dashi and seasoning, then adding the kamaboko. That way the tofu gets reheated and the scallions get very slightly cooked, but the kamaboko can still be arranged very prettily in a fan or something.
If you love the tofu and hate the kamaboko, you can double the tofu. Add the dashi at a near-boil, and crack an egg on the other side of the bowl from the tofu. Put a lid on the bowl immediately, and wait a minute or so before removing it, so the egg sets. This is sometimes called "moon-viewing udon." You can also just put in lots of tofu and scallion and have kitsune-udon (fox-udon: fox spirits love fried tofu, apparently).
Good luck!
