ok, each memory saves a panel setup, as its name implies. If you save a new setup, it will obviously write over the previous setup, leaving the last one you saved to be recalled. That's why you have 104 panel memories available with each load.
the 2nd answer is yes, in a couple of ways.
if you use just one voice save the panel memory with R1 conductor On and R2 conductor Off. Then on recall R1 will play, but if you have saved R2 with your choice of voice and volume with its conductor Off, it will still be recalled and can play simply by switching its conductor On.
Thus you have 8 setups from 4 panel memories (many more if you include the combinations of Left and R1/R2 both on, technichord, DSP etc you can prepare and then switch on after the memory is selected.)
All of this is described on page 9 of the 'How Do I?' book.
Also: choose your style as above
menu\composer\pattern copy\ copy ALL to composer A
now save the 4 MSA settings as above but then re-save each pointing to the composer variation rather than the original preset style variation.
memorise your choice of pad banks you talked about in each memory too and then
menu\composer\custom style copy\ copy bank A to custom style 1.
all your personal registrations and pad selections are now played from the custom style with MSA on, using the 4 variation buttons with no panel memories required at all.
All of this is described on page 42.