Honestly the vast majority of the time, for Inner Sphere tech, even PPCs will be able to threshold a lot of stuff; 91 armor is a pretty big investment.
Basically, your big targets to hit, for ASF armor, are 41 (the lowest you should go), 71 (which handles Large Lasers) and 91 (which will handle PPCs. It's *generally* not practical to get to 151 for gauss/cERPPC immunity, as that tends to cut your available weapons payload to an unacceptable degree.
Weapons wise, lasers, Particle Cannons, and plasma are very dominant, with Streak missiles also being notably very good; Autocannons, meanwhile, are worthless outside the basic AC 20 for maximum thresholding against DropShips - LBXs are forced to use Cluster rounds with the very high damage reduction that imposes because of how those are handled in Aero, while RACs and Ultras are hard locked to their maximum fire rates, with the heat generation, accuracy penalties, jam chance and high ammo requirements that imposes.
One should also generally avoid armor with special effects (reflec, ferrolam, etc) and stick with the Ferro-Aluminum in its various flavors- the Squadron rules (which you will be mostly using in a space battle) don't apply any such effects, only caring about raw points.
The really important thing is to remember that ASF can't do "Speed is armor"; the only way that applies is being so much more manuverable than your target that you can keep entirely out of its firing arcs. Which generally needs a 5 or greater advantage in Safe Thrust, which... Is not especially practical, and even then a gamble.
Combat between ASFs tends to be short, sharp, and leave the looser getting buried in a shoebox with what's left of his bird.
