Is there any opinion on how much impact the UASF will have? I mean will it really change something if I, as simple user, running a full node, "enforce" BIP 148. Do the users of the Bitcoin network have any power? Can it really "enforce" a change?

I heard that for Litecoin the UASF worked. But I dont know why. Is there any possible technical description on how this UASF works?

How much "voting power" has a user and how much "voting power" overall is needed for BIP 148 to happen.