There's a bloke very close to you, lives in your street actually! You might know him he's called Kev Nash

It isn't rocket science, you would probably find with a bit of time poking around inside it you could do most things. I'd say the only people who shouldn't mess about inside their machinery are those who are a complete liability with a screwdriver in their hand. Anyone else would get the hang of it pretty quick

There really isn't much to "service" inside a portable anyway. Vac motors are either working fine or blown and you replace them as a unit. You might want to check the carbon brushes which a 3 year old could do.
Pumps - don't know if yours is a simple diaphragm pump or bigger piston pump but again they're just a few bits you take apart and put back together again with new seals (piston pumps) or a new diaphragm, whichever applies.