There's room for flexibility depending on the desired tax strategy.Once you have more than a few properties, you'll want to consider software.

First he needs to decide what he needs and what he desires. 

Compare those owners with younger owners who have higher incomes and more desire to build large reserves for the future with the older folks who won't see the future and you can see the problem.

Do you have the time/desire to be a PM for others? 

On my end, I would never purchase a property that won't produce at lease 1k in net cash flow, and it must be in a desirable area that is expected to appreciate.

I put in my lease terms that I'll be asking the guest 30 days before their lease is due to expire whether they want to extend (IF they've been a desirable guest) and give them first dibs.

My tip would be to buy properties in desirable vs "affordable" areas.

I understand the desire of some people to have paid off houses, but you need to remember it is never really “free & clear”.

One metric they provide is new construction sales, which I can use to calculate % of total sales and see whether that value is trending up or down.My question is, in general is a market more or less desirable if there are a lot of new builds hitting the area? 

Some will do but they tend to be far and few in between and the terms are not very desirable at all.Another options is to take down the properties with a bridge loan.