There are several options, ranging from a simple agreement to establishing a Real Estate Holding entity and an escrow account to protect the funds. 

New flooring throughout, 2 completely redone bathrooms, took down walls to open the place up a bit, new doors, fresh paint, some crown, lots of patching, light kitchen remodel that include granite tops and an island with concrete top, new dishwasher and range, new HVAC units, moved some electrical around, new garage door, some fresh landscaping, added a fire pit, and gave the porch a facelift with some new posts.

I cannot answer your question about square feet amount to range on a SF cost of apartments but that really matter I you have a deal or not.  

I don't know wha market you're in, but 42k would be enough to buy a home in the 200k range.

.$450K house in Dallas is not considered as investment category. i recommend to sell and buy house in 150K - 175K range with rent in 1400 - 1600 range... following are disadvantage of renting 450K house...You are getting >0.8% rentMaintenance like repair/carpet/paint will cost lot more in higher value houses.

Is your property middle of the road with respect to other rental comps, or is it at the top of the price range.  

If yes, my price range is around $200-400K based on availability of down payment.When should I consider a 1031 exchange of the existing Colorado townhouse (3/2.5)?  

The latest quotes I'm seeing come at 5%-6% range.

The house I am interested in is listed to sell at $182,000 while other houses nearby (comps) are at around $140-$150k range.

@Sam Hiatt depends on what price range you are looking at, but my threshold is anything with that cap rate and >=$300 cash flow per door.