1. Not really. Not if you want similar performance (almost
) as your electric. It would mean a starter box isn't needed, but pullstarts break all the time, and one-way bearings fail regularly. These aren't cheap either, so after a very short amount of time you'll have spent the amount it would have cost to buy a starter box in the first place.
2. It depends on what 'reasonable price' means. If I were you, I'd have a look at the RB K9 engine. It's RRP is £199.99 and performance wise, it's meant to be in between an S9 and a WS9. Pipes and stuff are on top of though...
3. They are universal fitting so they'll fit in your 801.
4. Why do you want nitro now? The whole point of electric is that it's the future, and we're moving from nitro to electric, not the other way around!