I am interested in flipping homes and gradually building a portfolio of rentals.

If a "currency war" occurs (and this isn't alarmist, there was a good story on it on CNBC over the past few days), things could change rapidly again and then, yes, we would be in a bubble because rents likely couldn't increase fast enough to keep up with the increase in the cost of financing that would occur due to weaker currencies.But if interest rates were to increase more gradually, then I would say we're not as "bubbly".

Rising property tax at other states may eat into cash flow gradually over time...this point never crossed my mind, or not yet.

I've bought one or two properties where I fixed them up, but the numbers didn't support a full rehab so I told myself that's fine, I'll just gradually fix it up over the next couple of years.  

Second, in order to get to that point, you've got to gradually work your way up to it which means your personal time becomes less and less until you're ultimately able to quit your job.  

Gradually 3 of the 4 tenants moved out and the one remaining tenant has signed on 3 new people to move in without my authorization.My tenant has paid on time and not been much of a hassle so I would like to give him a chance.  

Sub-meter the water, and bill water + sewer costs back to the tenants:New tenants pay 100% of actual usageWould likely have existing tenants (on MTM leases) gradually pay more over a year until they're paying 100% of their actual usageThe property currently has a waiting list for vacancies, so I'm not too worried about a bit of turnover.I've found someone local with experience handling the items in (2) above, who charges $33.33 per month per unit, when occupied.

We've been reducing it gradually but haven't finished all the cleaning and repainting yet.

With existing low maintenance tenants I raise a little at a time and bring them to market gradually.

I totally get how this happens, because it is a slow, very gradual evolution - first its a short delay combined with a good excuse and a solid promise, so you go with it.