I don't know the full answer, but I can give you a handful of pointers.

• The mailing list is a good place to discuss Bitcoin Core implementation specifics, especially non-trivial changes. (It's not a good place for arbitrary questions / thoughts about Bitcoin Core....)
• The coding guide is an essential read.
• There's also a lot of discussion that goes on in the GitHub repo, especially in pull requests -- if you're thinking of implementing something, I'd check here to see if someone might already be working on it, or if the idea has already been tried but had some issues.