I've never bothered with a genny myself on domestic work as most properties you will need access anyway so jobs are best booked in when someone would be home. Not only that they can see you are doing the job and get paid there and then too.
Obviously if you go for a 110 volt vac using customers power you would need to hump about a step-down transformer big enough to take a constant current of whatever draw on the vac which I found a real pain in the arse too.
Regarding wanting a genny then to be honest if you don't do a lot of large jobs where you really need one then you might just as well hire one when needed as they are cheap as chips. Just add the cost of the hire plus added fuel cost for the genny to the job so you are not out of pocket. By the way a genny is rated in kva so it's not going to be as small as you think as you need to get one that has a larger max constant output than needed or it will be not fit for purpose.. Likewise you will need an 110v outlet on the genny and extension cables if using an 110v wet vac.