Any idea what I should estimate for costs?

First, you should have known your leases were up for renewal, and addressed it.Second, the buyer should have required estoppels for the leases, most don't, but your listing data Definitley should have shown lease periods.Third, we have no idea what your contract says about this, nor what your listing information detailed.

How do I get some idea of the average days on market in particular markets for house sales without asking a real estate agent? 

As a Realtor, I will tell you I have never had a pre-listing appraisal done on a property but in your case it could be a good idea.  

Do not hesitate, to post questions and bounce ideas around in applicable forums.

Once you have a budget and an idea of what you can realistically save annually, then weigh your options in rei.Please remember, the market doesn't care about your timeline.

I'd buy my primary home from him but we just had different ideas of rentals.

One idea I would like to add to what they are saying is, if you are a single guy, another route would be to buy a house that has a guesthouse in the back and then rent out the main house.  

Customizing your message is going to work fine for you.This brings up an idea, perhaps BP can "certify" a Pro Account user who has been on the site for at least 12 months and has a clean record.

It's not perfect but it gives you a rough idea of the value of a remodel.