Some people just use a straight 20% or take land value from county tax assessment. 

Taxes are based per 1000 value assessed.

The developers announced a $20k special assessment to the remaining homeowners and just recently announced an additional $5k.  

Is any of the 'profit' eaten up by repairs, assessments, R.E. taxes, income taxes, etc. or is it free and clear? 

Also important in IL to look at what the property's current assessed value is bc in IL the sale price could result in a double or triple of property taxes...

Hey BP,As I have started explore other markets, I am having the hardest time gaining/finding access to the tax assessed value of the properties in other counties/ areas.  

There are internal heating and cooling systems, electrical components, hot water heater, plumbing fixtures and a myriad of other issues that are hard to assess for the average home buyer.Realize that you are not going to catch every single flaw or defect on your first run through a home, although there are a few key areas that every home buyer should look at before making a decision.

That is how you need to assess the value, not by what one other property sold for.

- In PA, I can hold for up to 30 days, should I use the security deposit to assess damages and wear&tear, then give them the remaining?

It is up to you to decide depending on your assets and your threat assessment what level of protection will make you sleep better at night.