Accounting, CPA wouldn't hurt either.PM teaches you so much about vendors, and bids, pricing, value, budgets, tenants, etc.

Contractors appreciate you giving them as much info as possible before they give you bids. 

If the PM takes the time to format it the way I want (Pictures, competing bids depending on cost) I can usually give "Potty Approval" by text or email.

Always know the area of what you are bidding on. 

I try to have my bids in on deals I like well within 12 hours of it coming on market.

My recommendation would be to have a few GC's to give you a few different bids.

I am not familiar with NJ regulation of oil tanks, but here is a breakdown of how the bid should go

This may be a good consideration when searching for a condo, as contractors will give you a bid based on the difficulty of the work, as well as the requirements needed to get the job done.

In which case, I would need to get bids on total tear down plus stick build, utility hookup, etc.

A good contractor shouldn't charge you anything for a bid.