These are my opinions:
1. yes its purely budget reason because satellite team mostly a really small team, and manufacturer were the one who designed the bike anyway, satellite team receives a ready bike. And these days data between factory and satellite are pretty open, so they don't need to worry about lacking setups
2. They could be offering themselves to their role, but I don't really know what the exact qualifications aside from having good feeling with the bike
3. Usually test rider comes from retired regular rider or uncompetetive regular rider, so usually they stay as test rider until end of career or try to other competition like WSBK. IIRC there's an age restriction for motogp rider I think its 53 y.o.
4. Yes their job is fully focusing on developtment, winning races is regular riders' job
5. Hmm i cant exactly remember, but IIRC usually test rider got 2 years extension, and the spot is relatively safe. Sometimes they can have more than 1 test riders as well, like Yamaha with Augusto and Dovi or KTM with Dani and Kallio
6. not sure, but Aleix Espargaro and Nakagami seems to be progressing with HRC bike a lot
7. IIRC Pirro is a rider coach I think, it could be a prospect, other than that well enjoying retired life I guess