Or should we wait until after the first year to have roommates?

We still get Tenants adding a roommate or a pet.

Is it possible for a buyer to use the rental income that would be generated by roommates to qualify for a conventional mortgage? 

I'll be moving in immediately, and since there is basically no rehab I'm looking to get roommates in there ASAP to get the cashflow started. 

Potentially using FHA or conventional loan to buy the house I’m currently renting with roommates or buying a duplex and maybe moving in once my lease is up in a little less then a year.

The minute the couple breaks up or roommate moves out.

I have a really nice 2BR/1BA apartment in one side of a duplex that seems to be attracting a disproportionate qty of calls from prospects who are roommates/friends or a BF/GF and another friend.

It's in the same school district as the first house but much closer to campus (we live in a college town) so will be more appealing to renters, large enough to convert from 3 to 4 bedrooms and/or add a 3rd bathroom if we want to do so, and would be easier to list on airbnb if we wanted to rent out one of the rooms that way while we were also house-hacking with 1 or 2 long-term roommates.

If you do choose the REI route, if a crash happens have your son take a couple roommates for $400/month, Air BNB it for the summers when school is out, put up solar panels, figure something out. 

With multiple room mates, when one leaves, the landlord retains the full deposit until the last tenant departs.