Hi Tymish

The more ram that you have the faster FSCK will run,
Just remember to run a memory test before fsck.
FSCK will move data from disk to ram to fix it
if you have bad ram it will corrupt your data


as for volume size, you can always expand the LV size but you cannot shrink a LV.
MAy be better to start with smaller LV and then expand them as you need to.