you need to remove the LHS engine casing to remove the starter motor. Unless you're planning on this then you'll not be taking the motor off. If you do remove the starter, then there's two bolts internally and one external. Main problem with it can be that the cable from the solenoid can get corroded at the starter connection. When you undo it, make sure the mounting doesn't turn with the nut. It can break the mounting inside the motor, then it get's fiddly.
Only thing I would suggest with the starter in situ is that as you lower the motor out of the frame, be careful the lump doesn't fall on the starter. This would hurt it............