Downside is no tax write off but it’s a great option for truly no work passive income.

It was built in 2001, just had everything replaced and redone,very sizeable everything, it really is the perfect classic 4 unit townhome for house hacking.. current tenants are all Month-to-month, all but 1 have been there for 7+ years, 3 of them are section 8.Downside: Property does NOT currently Cashflow with me living in it, however if section 8 tenants are raised up just to Current Market rents it will cashflow abt 300 easily, and if I rent by the room for a very conservative 600$/room it can go up to 1866$/month.

By thinking about all these up and downsides, and playing with spreadsheets to see how they each impact your total return, you'll be able to compare two investments (an SFR in SoCal, and a triplex in FL, for example). 

One downside I hear about them is that they are loud but only for the time they fill the house with heat.

A higher down payment also means she doesn't pay PMI and she would get a better rate.How much downside is there for my future deals if I'm not on this mortgage.

I focus on my niche, what I think I know pretty well (and only time will tell if I am right), and try to minimize my downsides by buying at conservative prices, or leaving more cash behind, or having a specific exit strategy, etc. 

Down side, My cash is held up in my multi family properties that are being renovated.

Tenants stay till they leave, M2M allows a landlord to control their behaviour until they do.Defiantly no down side to a M2M lease policy.

What's the downside of it?

If she agrees, there's very little down side.