Perhaps the answer to this question depends on the purpose of the sign - is it for the benefit of the tenants in case any issues?

Is it true that in cold environments some tenants of old houses will board a window for insulation purposes?

Not exactly sure what line of work you're in now but as a caveat if you have no other source of income, do not leave your main stream. 

My main objective for signing up is to learn about real estate investing and specifically multi family.

This is how many turnkey properties are sold (aside from hucksters in NJ), and is the main reason why those properties don't appraise for selling price.  

My main concern would be the vacancy between tenants, and cost associated with a tenant moving out like paint and cleaning.   

I would be very careful commercial in small towns can stay vacant for EVER and a Day.just drive through any small town between Dallas and New mexico.. look down the main street.. nice brick buildings 90% vacant then on the outskirts of town a walmart and the associated fast food joints..the resi might work.. and maybe you change the commerical to cheap storage but put NO value in its cash flow would be my advice unless there is some compelling reason you think those would be leased.. if there was demand they would not be vacant would be my thought

And my main driver an investment is what CoC return is.Now with that said, I have started to look at more investments with a lower CoC (as I have more financial capacity now) and a higher IRR.

@Allan Yau still doesn't work, maybe it is blocked for potential virus purposes.

My business partner is a real estate agent who is also new to the investing side of real estate, and we are mainly interested in buy-and-hold for multifamily properties in central/south Jersey.