Vegetarian japchae recipe, could someone advise?

I have been curious about japchae ever since I saw it featured in a Korean drama that a colleague recommended during our lunch break. The sweet potato glass noodles are available at a Korean grocery store near my office park, but I am uncertain about achieving the correct balance of soy sauce, sesame oil, and sugar without using the usual beef strips. Could someone advise on a good vegetable combination that mimics the texture variety, perhaps using shiitake mushrooms and bell peppers available here in Bengaluru markets? I would also appreciate guidance on whether the noodles should be soaked or boiled first, as I do not wish to end up with a clumpy mess. Any tips on seasoning ratios would be most helpful.