I don't have four residential loan slots left.

You can have 10 conventional mortgages in your name, a spouse can have 10 in their name. 20 mortgage slots available for a married couple.

I am in the process of considering property management software and wanting to hear from others how they got a good majority of their tenants to switch to paying rent online instead of writing checks.As we have rental offices at our properties, most tenants just drop off handwritten checks there (we even have a mail-slot for after hours), so there isn't that much work involved.  

That is unless you make enough cash flow to hire someone to empty those coin slots.

Once you get 10 on the books, then roll the majority of those to a commercial blanket loan, and open up your 10 Fannie Mae slots again.

I'm guess the upside is vacant slots infill, and about half your expenses were labor (guessing that's the owners take).

You can each have up to 10 loans, so if there are 4 of you, you could have potentially 40 properties collectively before being out of Fannie Mae slots.

So rather than buying 10 properties together, you can each buy 10 properties for a total of 20 properties.At that point you roll most of your properties into a commercial blanket loan, that thereby frees up your 10 conventional slots again, so you can buy another 10 at the best terms.

I have a STR by a hospital and every slot gets filled.

Once you have hit your 10 limit, you would then move on to either Non-QM  / portfolio loans, or you refinance most of your properties into a commercial blanket loan, thereby freeing up your Fannie Mae  / Freddie Mac slots for a new round of 10 loans.The caveat is that when you do the Non-QM / portfolio or the commercial blanket loans, that you are not required to have a personal guarantee on those loans, otherwise if they require a personal guarantee, then the still count in the 10 financed property rule.