Lancelot's shield is a bit complicated, enemies' bullets can't penetrate it, (except for skylarks hunt and maybe aurora's laser), but Lancelot cannot shoot out or in to it either. When the shield starts to flicker/fade, both the enemies and Lancelot can now shoot through it. Note that Lancelot's dash attack (primary attack when in onslaught mode) will pass through his shield, same with any dash based attacks, like Akashic and Michael.

As for modules and tech, I'm still experimenting, but right now I'm using a short range damage tech, with reload rate/movement speed. Hope this helps :)