Do you mean to reach Black Order MB or what to do within it?
BOMB is kinda the least important thing to do strategy wise. It's only points, it doesn't make any other progression; you can't progress the grid or avengers or combos or super modes or anything. You can win the Soul Gem if you didn't have it, but that doesn't require much strategy, just light and get the jackpot then the super. Actually the one thing you can progress is the Capt Marvel ramp count-up, and I often do hit that 5 times or so during the mode.
Really the biggest strategy for BOMB points is to have the Reality Gem on Captain America ahead of time, since the super jackpot is always there. Besides that, it's all about ball control, catch everything you can on the right flipper and make all the shots from the left (everything except Hulk.) Do aim for Capt Marvel each time you qualify an avenger, since that shot increases the jackpot multiplier, but doesn't stack if you qualify more than one avenger.
I generally risk the Soul Gem for the multiball restart only once I've already collected the jackpot so I'm close to the super, or else if I drain the last ball during the 15-second grace timer. Of course if you've already collected one super, then the Soul Gem is risk-free.
Regarding Widow-Marvel-Iron Man combos: This is very effective with Black Panther's level-1 ability (ideally held there by the Power Gem), since after the tower drops the ball, it happens very often that you can get control on the left flipper fast enough to shoot the gauntlet ramp while the combo is still lit there.