Welcome aboard.
Can't help you with #1. both my 153 s are portable
#2 OH yea, those flat spots have caused many a machine to get thrown out because of the shake and racket. Glad you are saving yours.
#3 yep 8 is max on reverse, 12 on forward. I just checked.
Does yours have an MG in front of the serial #? if so it is magnesium bodied.