A few minor factual errors here. First of all, the UASF itself will not split the chain. The chain will only split if 51% of miners choose to cause it. Of your “two likely outcomes”, the second one is not realistically possible: so long as the BIP148 chain has significant usage, it will eventually overwrite the miner-split chain. The only way for the miner-split chain to survive is if nearly the entire community were to reject BIP148 (which would entail current BIP148 supporters giving up).
That being said, those things probably don’t actually influence your course of action, and I applaud you for making plans to protect your customers’ bitcoins in the event of a split.