Yes, Tyranids follow normal rules for being Crippled. In addition, Massive Claws and Feeder Tendrils may not be used if Crippled, but are otherwise unaffected by SO's.
As for moving while grappled, it depends on relative sizes of the ships involved. If both ships are the same size (Escort to Escort, Cruiser to Cruiser, etc) neither vessel can move. If the grappled ship is larger (Cruiser grappling a Battleship, etc), the grappled ship may only move 1/2 speed and can't turn.
In any case, both ships can shoot, but at half strength, Nova Cannon and similar weapons cannot fire.
I'm assuming that the Ork versions works in a similar fashion, but I wasn't involved in the Orks development so can't tell you with any certainty, sorry.
As for the Bio-Plasma arcs, F/L/R was the intention. My experience from playtesting found the range to counteract the ignore shield ability. However, more feedback is always welcome. Maybe making the port/starboard BP L/R may be a good thing for the capital ships. Iwould leave this for the escorts however.
Hope this helps! And keep it up, sterling work!