The chances of getting out and then rejoining as a Para are very very slim especially in this current climate. To get a trade qualification, the Army will invest several thousand pounds worth of training on you and will expect a return. That means doing you job at trade.
If you want to do P Company then do not become an aircraft technician. There is no need for parachute qualified Air techs and as such you will find it incredibly hard to get loaded onto a course.
So, you are in a quandry. On one hand you want to be a para and on the other you want to be a tradesman. Yes, you may well be both as a VM. However, are you really sure you are tough enough to pass P coy? Because if you aren't very good at trade and very fit they probably wont consider putting you into a Para Regt from finishing your VM course.
Another thing is that you are talking about getting a trade as it will be good to leave with one. Well, true you have more chance of employment with qualifications but who says that after 9 years or so (estimating a time that you would be in) you would still want to turn spanners? Im a technician and nothing would horrify me more to be doing that once I get out. (Hopefully you get what I mean, im not trying to say look at me or to say that everyone is like me).
The Army will give you lots and lots of transferable tools that you can take to civvy street and you can also study once you are in to gain other quals.
Hopefully this has given you some food for thought. I think you should try to get some kind of work experience in both the Para and the REME before taking any further steps as it will help you no end.