A1:When you complete a level, click on the save button. Also your game is auto saved* when you start a level.
*This only works if your PC stays powerd on and is also unreliable so make sure to save regularly.
A2:Because of the performance limtations and visual glitches.
A3:Just run the new installer.
A4:No.
A5:No.
A6:No.
A7:Nope.