Q631
If i take the martial study feat, and i have levels in an initiator class, does the maneuver gained become part of my maneuvers known for that class (and subject to it's maneuvers readied limit)?
Yes.
What if i took the feat several levels before i had levels in an initiator class?
They will be tracked separately. Let us use a fighter4/warblade1 sample character to illustrate this. Say at fighter2, 3 and 4, the player took martial study 3 times to gain the use of 3 1st lv maneuvers (steel wind, stone bones and charging minotaur). He can use each 1/encounter without no option for recharge. He then takes 1 lv of warblade. He gets 3 more maneuvers known and 3 maneuver readied slots, which he can use to ready only the 3 chosen via warblade. He cannot opt to select maneuvers already selected by martial study earlier on (in this case, steel wind, stone bones and charging minotaur), nor can he ready those maneuvers via warblade slots.
You have to decide if extra maneuvers available is worth not being able to refresh them during combat.
It is a fairly effective way of giving monster npcs a lot of maneuvers for a low cr increment (have it take martial study thrice prior to a lv of martial adept). At +1cr, you get the use of 6/7 maneuvers.
Q632
If i take the martial study feat to gain a Shadowhand maneuver, does that allow me to spend maneuvers or stances gained from later Warblade levels to get more Shadowhand maneuvers/stances?
No. You are still limited to the 5 schools listed for warblade.