Underestimating the cost and time of renovations (usually with limited reserves to work with) and overestimating going rent rates.   

You should have more than enough equity at that point to have all your properties under one reasonable loan and still have cash in reserves for repairs that may be needed.Of course, I'm not a lender or lawyer, so my advice is limited to my experience as both a Realtor and appraiser.Hope some/any of it's usable.

Louis Federal Reserve, average 30 year fixed mortgage rates are still under 4%.

There are a bunch of new services that give commission advance to Realtors for a hefty fee, which would further confirm that most Realtors are struggling and not able to own rentals 

You also need to take into consideration ongoing maintenance expenses and property management expenses, as well as expect to have some vacancy and have a reserve for that.

I think that's the advice I've been looking for; confirmation that I'm not crazy and being too conservative.

Can't confirm if it will respond to a cycle programmed with the door open.  

They will also apply a 5% management fee and 3-5% reserves from the net rents (gross rents - vacancy).

slightly off topic . in Hawaii, while on vacation we heard some loud yelling and and what sounded like a lot of domestic violence happening - I went outside and was trying to determine the location of it and soon another guy joined me who had also heard it - we discovered the room it was coming from and both approached to ask if everything was ok - a big muscle bound guy answered the door sweating and breathing heavy - he said everything was ok and that him and his girl were just having a disagreement -when asked if she was OK - he said yes - then the guy that was with me asked she could please come  outside and confirm to us that she was OK - I was a little taken back by his boldness , but was glad he asked - so she came to the door and confirmed she was OK and didn't need any assistance.

If you send me a private message I'll try to remember to send you the details when it's confirmed.