I think your ProtoMech points will vary depending on the rest of your force composition. You want to compliment what the rest of your force already brings to the table, without going overkill.
Say you already have one big, bad holepunching 'Mech with Gauss Rifles and ERPPCs. Back that up with some ProtoMechs with SRMs for some critseeking, and bring some Inferno rounds as well for anti-infantry or anti-ProtoMech duty.
Then maybe grab something with good LRM durability to lay down some smoke rounds or something, and something else with ECM or an Active Probe depending on the ruleset you're playing with. Then you can end up with a mixed ProtoMech point of, say:
-One Hippogriff (smoke support, anti-tank work)
-Two Orcs (inferno support, anti-infantry, anti-BA, anti-ProtoMech)
-Two Minotaurs (bodyguard duty, direct fire-support)
Replace the ProtoMechs as needed for ECM (Roc 4), an Active Probe (Satyr), or TAG (Satyr 4). And on a larger scale (say, Cluster size like Kojak), instead of fielding mixed Points, you can field pure ones to achieve pretty much the same result.