Like the guys who do the turnarounds at your average airport, what quals./experience does one need for that?
And aircraft refueller, how does one get that job
Lets clarify your first query. " the average airport"....give the range from say LHR to Wick, there's really no such thing as a "average" airport.
As for the "guys doing the turnarounds", well that depends entirely on the operator. The crew may well do their own transit checks but with handlers doing the chocks, ground power, start up and see -off / headset for example.
However, a Line engineer may also be present with some operators and if you think that Line engineering is simply about pitching up to an aircraft, doing a walk round, then signing the Tech Log.....with a free coffee and sandwich from the Cabin Crew in the process, I have some bad news for you.
You have, I take it, seen those same guys at say, 03.30 hrs, in the middle of January in inclement weather working on the aircraft ?....the short answer is clearly not.
Quals ?.....formal and recognised engineering training, a Licence and...several years experience.
As for the refuellers, lets start with an HGV licence, an ADR qualification thereafter ( plus a few others ) and, again, experience.
To be honest, I think you are letting your heart rule your head here and I think it's safe to say you would never get a job as a Line Engineer. I also feel you are not really prepared to listen to advice until you get the answer you want to hear.
Sorry if this sounds rather blunt, but, there's no other way of answering your questions and, along with others who have responded, offering you realistic advice.