I'd break up the deposit into two payments in two months, max.

This greatly increases the likelihood that they will break up some time during the tenancy.

My fear is if they break-up then GF can't afford rent by herself.What should I do?

Try to break-up the fee by phase.

Sure.Is it hard to break up with the girliefriend when you find one with bigger rounder juicier...

I think what I might do is get the concrete done in the spring, and have the actual garage built in the summer to break up the costs.    

What if they break up - and she decides that due to his abuse she needs to flee the home.

Hi Kyle,I own an 1850's multifamily in the Boston area.Gas -- Would be tricky to break up since it looks like you have one furnace and one water heater.Electric -- As mentioned, if you have sub-panels for each unit you could have an electrician and your local utility company install meters.

I breakup my rental income in few buckets after servicing mortgage.

Well they made it through one unit before the break up.