With almost 1000 full scale carrier takeoffs and landings I can tell you a few things that I have observed and how they would apply to models since I am a lifetime modeler as well.
Modern catapults are about 300 feet long and are steam powered. The forces on the full scale(FS) planes are unbelievable! At the next airshow go and look at the difference between the service aircrafts landing gear. The Tomcat gear has a draw bar on the nose gear and the shuttle will pass between the nose wheel tires. The drag link on the back of the nose gear is the major load carrying part of the nose gear assembly. I don't think this system is easily replicated in a model and I would shun away from 3500psi. The volume of high pressure air required would be a large bomb without the proper safety proticalls.
I would suggest the high start method of launching with attach points on the bottom of the airplane. Maybe a dolly on a track to sit in so that the landing gear doesn't catch in the high start. This could be set up to accelerate to take off speed and then the plane would takeoff under its own power or another system were the plane would be pulled into flight more like a glider set up.

For landings a tail hook that is scale would be very difficult to make strong enough. I have alot of experience with prop planes and arrested landings and I would suggest you trying that for a while.
The weighted bags and string works ok. It would be best to plan to land prior to the wire and roll into it for a model jet set up. one problem would again be the wheels catching in the arresting gear.
You could use the Barrier setup like the Air Force does full scale. It is in the overrun and about 2 feet high and if the plane gets that far it will bring it to a safe stop although some damage to the plane may occoure.
In the models it is like having progressivlly taller grass at the end of the runway.
If you have any further questions you can email me on or off line
Sparky