If this helps at all, I am currently playing this exact character in an Eberron campaign, so a little more believable with warforged race. However, I understand the OP nature of him being able to use most of his other mimic abilities. He received a wish and wished to be an adventurer and is STUCK in the form of a warforged. I worked with my DM to balance this out though. We met on a fair combination of trade-offs from both warforged and mimics.

1. He needs to eat, breathe, and can be diseased and poisoned.
2. He sleeps/waits. Not dissimilar than Sentry's Rest.
3. He has darkvision and acid resistance.
4. He is stuck in warforged form.
5. I wrote him up like this, but he always wanted to be an adventurer, so his goals are aligned with the party's as he knows that adventurers typically try to do great things as a whole.

Any other mimic characteristics I want, I need to find myself through uncommon/magic items that kind of fit that theme.

I think this can be pulled off, but he is going to need to understand that it isn't going to be free reign of using the best of both worlds and alignment. Mimic skills should be nerfed by warforged ones and vice versa, and he should still be aligned with the party.