I'm now considering expanding my real estate ventures into building custom homes, but I know this is an entirely different beast between the required capital, learning curve, time committment, etc. 

Let’s say you own 1/2 of the $700k property as a TIC and can do a 1031 easily.

I currently own a 4-unit in Allentown which has done quite well for me and looking to expand my portfolio throughout LVH.

If they are professional, they can explain this quickly and easily.

The initial plan is a 1200 sf build out with plans to expand back away from the cliff later as finances and interest rates are more favorable.

If you spend time learning how to manage well, your income will increase, you'll save time, and you'll maintain your sanity with the courage to expand.

This is something that can easily be changed later if needed.

The only time I'd say it's an okay idea is if either: The area you're investing in is expecting so much appreciation that you will easily profit off that (watch out for mortgage interest though...the appreciation needs to be higher than what you pay in that and expenses to make it profitable)You have some specific reason for wanting to do it- family ties, future home, major long-term hold, etc.Maybe I'm forgetting another one, but those two are all I have for now...

If you have the data easily available, can you give us cash flow figures throughout the 13 years? 

There is the tactical "act" of underwriting, then there is the much more valuable "art" of underwriting.The act can easily be taught.