I've got a 03 TF160, had it coming up for 2 years. When I first bought it I climbed underneath and was shocked at the amount of rust on the subframes, brake pipes etc.
Think the earlier F's had better underneath protection, so it doesnt follow a newer car will be less rusty.
If the engine, gearbox seem OK it might be worth cleaning up the subframes and painting up, something I will have to do sooner rather than later.
Not so sure about the body rust, but it doesnt look too bad, just if you can live with rubbing it down, treating the rust and spraying. Or panel/paint shop quote might not be too expensive and will give a better finish.
But to keep the costs down you will have to get the overalls on and follow the useful "How To's". Garage rates will kill it.
The cars are so cheap, its a matter of how much you want to put into them to keep them on the road. I went to buy a £1000. one but that had gone, they had another one 3 times as much, that the wife said, "better to buy a good one, cheaper in the long run". So I did. But..............still rusty underneath, just had it MOT'd and passed after replacing the two front subframe mounts. Originals just flaked away to nothing. Can recommend Brown and Gammons uprated ones.
So its really down to you and the love and cash, you want to throw at the car, if it grabs you, or not!!
by the way, plenty of help on here, if, or when you need it.
Try to clean the seats with shaving foam. Far better and cheaper than upholstery foam.