A good set of architectural drawings and a well drafted contract containing payment terms, time frames,  specs or at minimum allowances that is carefully reviewed by both parties will greatly reduce most contractor disputes.

I would like to start acquiring multi-family rentals but a) don't have a lot of capital to put in myself, b) nor would that strategy allow me to build a portfolio within a reasonable time frame. 

and were done by 100.00 incredments and by year time frames so if you wanted to know the payment on a 45k loan at 10% for 7 years you found the 10%page and then 40k ( went up to about 200k)  then the 5k the payment was spelled out and you added the two together to get the monthly payment..

Maintained appropriate insurance yourself (builders risk when under renovation, vacant when vacancy periods exceeded your insurance policies allowable time frame etc?

I have a bunch of buddies from my college/old roommates moving to Dallas to start work in the same time frame. 

Upon selling, you might position yourself to take advantage of some other deals that come up within that 1 year time frame, so you can have two projects running simultaneously, and so forth and so on. 

Then you present to the money:The purchase contractThe Rehab estimateThe comp package showing sales lst 6 months of same typeA breakdown of the financing, a term sheetAn estimation of close to close timeframe: Close the loan for purchase, rehab completed, listed for sale, close on the sale.An estimation on the cost of the entire project close to close a Calculation of their return on capital with a standard deviation calculated for imperfect exit - which is more of a normPresent all that to someone and now you bring a lot of value and you can even argue bring more to the table then just some dumb money.

Is it possible to purchase the unpaid taxes as a lien investment that will permit foreclosure within a specified time frame?

Timeframe?

The realtors, sellers, financing, due diligence, timeframe and process are all different.