Dont waste your time. The strategy is awesome, but if you play in PokerStars, their policy is that if you re-enter tables with minimum stack and leave when that stack grows, they will up your minimum buy-in. So read it, so you know how to play against a small stack, but play BSS.
To answer your questions:
1. you play like 9% of hands. And at full 9 men tables you have to play like 11% to not lose from the blinds. The MSS works, because there are alot of bad players, not caring if you play 20bb stack or 200bb and if u play 80% of hands or 2%. Also there are some bad BSS players that dont look at the size of your stack and make mistakes calling hands like suited connectors or low pocket pairs against you.
2. Ofcourse you should consider the lowest stack in hand as the effective stack. And cash is not like tournaments where big stack can pressure the low stack - actually often it is quite the opposite because MSS often play bigger variance game, stacking off with underpairs. To make an example:
40bb raises in the HJ
You call 88 in the BB
flop is T42r
He can have a JJ+, TX, 99, 88, 77, 66, AK, AQ, AJs with a bd fd and with this range hes most likely going to stackoff. Your decision with 88 is rly tough and high variance. Me? I wouldnt fold it even if my life depends on it, but thats just the gambler in me