Yes, the trailer is easily capable of lifting all tires off the ground with the jacks needed for any repair. No you would not need to lift the whole thing just to change a tire, but brakes and wheel bearings, yes.
The trailer is fine lifted, Oliver simply recommends not leaving it like that for extended periods of time, what that equals - you would have to ask.
Here is how it looked to replace the EZ Flex out and grease the bearings, it sat like this for two days, no problem, while I waited for inner seals to come in from Amazon (never did it before, didn't know) I didn't go in the trailer while like this, so nothing to report.