A $30k down payment is going to DRASTICALLY limit your pool of buyers.

Only reason I've been doing it is to get 0% business credit card limit increases.  

By diversifying, but still investing in the most promising deals, you limit the possibility of a devastating loss without limiting your upside.  

New construction in the city limits is increasingly hard to find and increasingly expensive.

Aloha Jose, as many have mentioned based on the limited info you gave there shouldn’t be any issues finding a lot of lenders.

Don't limit yourself to the San Antonio area, you may not find one! 

If you have a credit card with a high limit or a line of credit on the existing duplex that might give you some wiggle room.

@Brian Rocha -Something to note is lenders will oftentimes slightly limit leverage on the purchase of a hard money loan or a "fix and flip" loan if you are doing borrower funded rehab.

Lock-out, should they continue to not come even, would be typically less than 14-days.Unless the tenant comes even with the rent (which would result in dismissal of the non-payment of the case), there is generally limited defense to this process.

My humble advice to anyone attempting to do creative finance is:Creative finance is for experienced investors who have access to capital if anything goes wrong.Learn the lawsDon't use a contract "off the internet", laws vary by state and are also regulated on a federal levelLearn the financing techniques correctlyDon’t skip parts of the processDon’t ever do a “kitchen table” closingUse the proper deedAn attorney can help you with the legal work, but the rest you are on your ownYour guru will not bail you out“Investing” in someone else’s deal by providing a small 2nd loan so the “investor” can pay for “cash to the seller” and for “closing costs” so he can do the deal is a very bad planKnow what problems can ariseLearn the responses and solutions to problems before they are neededKnow everything there is to know about Title and what that meansKnow who a "protected class" individual isLearn the "back doors"Learn human natureUnderstand timelinesUnderstand regulation enforcement (some of these "mistakes" have a 10 year statue of limitations ( they can charge you 10 years AFTER you do the transaction) and carry hefty fines and possible imprisonmentThe court doesn't accept "I didn't know" for an answer"Know that the source of the lead plays a serious role in some states and federallyKnow how much of a "profit" pushes the boundaries to invite an investigationYou can be sued by the seller if you don’t do things correctlyYou are automatically at fault if an investigator or attorney or regulator gets involved.