@Steven Caligaris For #1, yes usually it is the seller's responsibility to pay both seller and buyer's realtor commission. But it is all upto your agreement with the seller, sometimes buyer can also shoulder the buyer's realtor commission if buyer has put that into consideration in the numbers.
#2 5% down, are you getting mortgage from Bank and you will be living in one of the unit in the multi-family? I see you also don't have property management, just take into consideration if you are ready to receive all the calls if there is any issue on the unit. You can check Rental and BRRR calculator here in BP. One thing to consider also if you will be retaining any tenants, do they have security deposit since if they left and want their security deposit back you will be the one returning that one. If you are not retaining, you might want to put some rehab budget to do at least repaint (clean carpet or replace carpet) @Brandon Turner has done a lot of webinar live examples how he have calculated numbers.