Okay, a couple of suggestions beyond what Miwa has posted.
1. If you want perfectly clear, light soup base, you need to cook slowly. Bring the pot to a near-boil, not a full rolling boil, and do so slowly: it should take about 45 minutes to come up to this heat. When it gets there, turn the heat down so low that you have to look closely to see motion below the surface. When you've finished cooking for 2 hours or so, strain coarsely (to remove chunks) and then very fine (to remove little bits of coagulated protein). Let cool to room temperature, and then refrigerate. When cold (12 hours or so later), remove any hard fat from the top. Now bring the stock to a rapid boil and reduce it by half. The result will be different, not necessarily superior, but this is something they talk about in passing in Tampopo.
2. I would definitely add pork bones to the stock: straight chicken isn't going to get the flavor you're looking for. Tonkotsu ramen is usually all pork, but not always.
3. Aku is coagulated protein, usually referred to in English as "scum." It is bitter and must be removed. The easy way is to use an extremely fine-meshed flat skimmer.
4. After the first half hour, there will be very little scum rising, and any skimming will be removing fat. If you're going to do the cool and chill thing, the fat will freeze solid in a refrigerator and can safely be ignored.
5. Another type of ramen stock is "milk stock," of which there are two kinds that I know of: with and without sweet white miso. To make milk stock, you must use some fairly large pork bones with marrow, regardless of whether you use chicken. Use twice as much water. Skim all the scum as quickly as you can. Add the floating ingredients, and then bring the stock to a rapid boil -- yes, a rapid boil. Put a lid on it. Now wait 1 hour, checking occasionally to be sure that the water level hasn't dropped below that of the ingredients, which is why you use the extra water. The liquid will be quite foggy, and should be reduced to the end-point, i.e. you should have removed about 3/4 of the liquid. Strain coarse, then medium, and only then fine -- and you may have some trouble getting it through a fine strainer. If you chill it, it will turn white and nearly solid. This emulsifies the pork marrow fat into the stock so that it will not separate out: very bad for you, but a wonderfully intense flavor.
6. If meat is inexpensive, use meat as well as -- or instead of -- bones. A bone stock has a less rich flavor. I would suggest this especially with a miso ramen.
7. Be very sure you are using fresh egg noodles: not everything labeled fresh ramen noodles has egg, and without it the whole thing will taste very unlike ramen.
8. I would advise against the procedure in the recipe as far as adding the seasonings. Mix up the soy and whatnot liquids as their own mixture. Put a generous ladleful into a bowl, add just-cooked noodles, ladle on soup, and then garnish with roast pork, half a medium-boiled egg, and lots of thin-sliced negi or scallion. If you mix the seasoning with the broth in advance, I do not think it will freeze especially well, whereas the broth by itself should freeze admirably.
9. Do freeze the broth, but don't keep it more than 3-4 months in a home freezer: a home freezer isn't cold enough to prevent bacterial growth longer than that, and since you're not freezing under a vacuum there will be oxidation as well.
(In case you hadn't guessed, I'm sort of a soup wonk.)
Oh, one last thing. NEVER NEVER NEVER stir the stock while it is cooking! This will release a great deal more scum, much of which is lightly stuck to the ingredients in the pot. This is why you don't want a rapid bubbling: the motion in the liquid releases yet more scum.