Ey up Steve, I've done a fair bit of both HFT and FT (and SFT too) so I'm probably reasonably well qualified to have an opinion on the subject.
First off, I'd say, don't rush into your scope choice. First thing for you to do is just plonk the highest mag scope you currently own on your intended FT rifle and spend a bit of range time getting your sitting position stable.
Believe it or not, but with some adjustments, practice, trial and error and a bit of observation of other shooters sitting position eventually you'll be able to get it very nearly as stable as a rested prone position.
My advice would be to get yourself to a club with not only some decent FT shots, but also a decent FT shot who is able to explain what it is that they do. and have a look on some of the photo threads on here from the 2013 GP series - there's some excellent examples of the different positions people use in those photos.
One of the biggest differences you'll notice is, shooting on high mag is quite a bit different to shooting on 10x mag - and it will really show up any stability issues in your positions, even to the point where you'll really be able to see your pulse if you don't get your points of body contact right.
Don't worry too much about range finding or clicking at the moment - plonk your highest mag scope on your FT rig, set it to say 35x mag and see how you get on with your sitting, standing and kneeling positions with it.
If you don't have a 35x mag scope - buy something cheap and cheerful (maybe one of those £65 BSA jobs) to give it a try.
You might discover that although you need 40x mag to range find, that you shoot better on say 20x mag or 16x mag - quite a lot of FT shooters shoot on a lower mag to what they rangefind on. And that's an option that isn't open to you if you go out and buy a fixed mag scope from the outset.
Clicking is nothing, it's a doddle. It's actually a lot easier than holding over! - there are a few little gotcha's you'll need to watch out for (going a turn out for example). Rangefinding by parallax will take you time to learn, you're probably looking at a learning curve of around a year to two years to get it consistent and learn the quirks of your chosen scope.
We're coming up to winter league season now, so it's the perfect time to try stuff out. Winter league shoots are nice and relaxed and no one gives a toss about what score you put in (apart from yourself)