Ensure that the purchase price, rehab costs, and After Repair Value (ARV) are all reasonable and accurately assessed.

I actually have done personally exactly what you're describing - HELOC on primary residence, use that to purchase new primary, move into new primary and rent the previous home(4 times in 5 years).

I recently received a quote to paint the entire interior of my recently purchased home.

Percentage of the purchase price), average home in Cleveland purchased in 2014 or the average home purchased in San Diego in 2014.  

I see this is an older post (better late than never) Usually 1% of the purchase price is reasonable.

2) Do you hire a property management company before or after you purchase the property? 

I am consistently helping my investor clients purchase move in ready 3/2/2 SFR's here for less than $300K.

If you can swing it and are willing to do what it takes to not lose the property if sh** hits the fan, then I would highly suggest purchasing in a more desirable area. 

I just purchased a unit in the Mount Vernon area close to Ft.

I am a licensed Real Estate Agent in VA so the process of finding the homes/purchasing is not what concerns me.