question

That's an interesting question and as always the answer is "it depends".

5000VA is on the order of 40 amps at 120 volts so finding a service to provide that is iffy. But you may need less from shore power. The closest would be a 120v/30a RV style connection.

If you need more than 3600 watts from shore power, you probably do need to look at transformers. You will probably at least need to support 120 volt single phase and 120/240 volt split phase services. A transformer with a 240 volt input winding and a 120 volt output winding with a way to bypass it would do the trick. If you also need to support two legs of 120/208 volt three-phase service you'll need "taps" on the primary winding to accommodate the lower incoming voltage and still produce 120 volts at the transformer output. With three-phase power you must not use a center tap because the two phases are 120 degrees out of phase.

Unless you have a specific need for isolation, an auto transformer is probably sufficient.

Here are some drawings that will hopefully help explain:

Isolation transformers would probably be needed only if you NEED isolation from incoming shore power.

Obviously, the auto-transformer could be completely bypassed in the 120 volt input case.