Recommendations for Finishing a Basement?

[Michael Mahung]

I am considering making an offer on a 3 flat in Chicago and plan to finish the basement.
Before I just jump in head first, I wanted to get some opinions from people with more experience than me.

What is the usual process for finishing a basement, what materials should I buy for the contractor(s)?
I've had some people tell me I don't NEED to pull permits, but I would like to get everything done right to avoid fees and issues if selling.
If I did pull permits to finish the basement (making it a legal 3-unit w/garden apartment), would there be any changes in the properties zoning?

The basement is a full-walkthrough with 8-9 foot ceilings - I'll link a couple of photos for reference.

Photo 1 - Potentially bathroom & bedroom

Photo 2 - Potentially living room & kitchen

Thanks!