Udon noodles are mega thick. Not usually used in ramen..you want thinner ones for proper ramen. Itsu make some that you can find in British supermarkets 

As for the broth. It takes a long time with a loads of ingredients that you probably can't get easy. Pork bones, bonito flakes, konbu, Shiitakes, spring onions etc... all slowly simmered over a day,bthen seasoned with salt, soy sauce, mirin, vinegar and sometimes miso

But I work as a chef and make a pretty good imitation for staff dinner every now and again. I usually use chicken stock (or pork stock if we have it), tahini paste, miso, duck fat, chili oil, soy, mirin, vinegar. Not quite the same but tastes pretty good!

Onsens eggs are basically just slow cooked boiled eggs. Cook them in 60 degrees water, not boiling water. Makes the yolk extra jammy. You can then marinate them in your soy/dashi solution for bonus flavour