First, you should know this varies by state.

I'm looking into purchasing a multi family, my question is ,I'm sure it varies by location, but  which would be a better investment 3/2 or 2/1 or 3/1? 

Not sure if that varies by state, 

People may vary and there could even be state rules on this ( check yours)..Visually..

Does anybody know, roughly, around that area how much tornado insurance costs (or if it is just normally covered)--or does this vary widely?

It varies from place to place, but I cannot help but think that what you have budgeted is too low. 

I've looked around at number of different providers who offer said service and quite frankly have found varying costs and reviews, some of which to the point I find shocking. 

Of course your mileage may vary.

I have a lot of home owner buyers that I refer to as "end users" in my database, plus I have investor buyers looking to rehab.Single family homes are a hotter product due to the requirements of banks to be more lenient about granting loan pre-approvals over condos/multi family.Compensation would vary based on if you are looking to sell on market or off market, and for off market, it depends on price.

It varies a fair bit by metro area, sometimes less than 10% (San Diego) other times more like 20% (STL, Riverside, CA).