3. Remember earlier when Han flowed away with a Star Destroyer's garbage? What was stopping Lando from doing that?
4. Maybe R2 ran out of fuel for his rockets or they got broke sometime in between 2 and 5? Technology can and does break quite often due to aging. I don't know if this one is possible because I am uncertain exactly how a droid works: maybe he ran out of space in his memory and wiped a portion of it to make new space and wiped his knowledge about the rockets?
3. Well we don't know if he knows that trick. But remember Boba isn't far away so they could just call him up. Or maybe Boba even told them what Han did.
Of course thinking back to that scene they weren't in a position to do it and the SD was just about to use the tractor beam when the MF jumped to light speed.