Denial  there was 60k of code violations as well I could have got those negotiated down to 10k or so.. but the seller would not cooperate so that money came out of her proceeds as well.. 

Ensure it is up to code.

I tried looking on Redfin for comps but I wasn't seeing any multis in that zip code.

The garage was converted and added to the living room/dining room area with a separate laundry room and all done to code. 

I live in grand junction Colorado with the first 3 digits of my zip code that begin with 815.

And then there's building code compliance - how hard is it to do, especially for a foreign-based design?

Currently studying my States Building Codes in preparation for the Contractor exam. 

Code requires access to your floor system so in pretty much any semi-modern home there is access.

Should I get an estimate from a home builder, see the zoning codes for the area, etc?

However from what I've seen it takes about 300 signs to get a contract and you'll want to keep putting new ones up each weekend because code enforcement will take them down.