Once you figure out if its even feasible from a legal stand point you can get estimates for the construction etc... to get your ROI. 

I haven't went through a transaction yet because I'm still new with a lot of questions and still trying to figure out where to start.

Closing costs came in at 14% instead of the 5% I budgeted for and I'm going to have to put up cash I reserved for "pretty things" and cosmetic improvements to cover closing costs instead.I'm trying to figure out if I can finance some closing costs on a 203K loan since my lender wouldn't let me do a "lender credit" and take a higher interest rate on a 203K.

You need to run the numbers on where it will make sense, you can figure 2 months difference in permit delays for both then add the "premium" you'll get for selling a 2016 vs 1920.

Trying to figure out how to find cash buyers with a budget of $1M-$3M for 3 Triplex's in San Clemente..

I ended up just going up there myself because I figured I can look for it as good as they can.

I figure to overcome fear, and actually see that REI'ing isn't as scary or intimidating as it seems, I actually need to buy that first property.

You just have to expect both and do not worry about that. 

If its something unplanned or higher than expected, we can also use it as a negation tool.  

As the tenant you are expected to negotiate in your interest (and review with your counsel before signing).