Speaking of which, Just how much stuff do you normally keep in your inventory? I keep running up against the 150 item limit. I do tend to be a pack rat and horde stuff. I guess I am scared of selling something I might later need.
Depends.
For weapons, I try to equip my squad with the best weapons and sell the rest (Shepard gets priority). Spectre weapons (HMWA VII and X) are the best. Once you have the Rich achievement, you can buy some HMWA from the Normandy guy and the C-Sec guy with any Shepard. HMWA X unlocks when Shepard reaches level 50.
For anti-organic ammo mods, I keep the best Anti-Personnel/Shredder rounds, about 3-6 each. Shredder stops at level VII and there is no equivalent at later levels.
For anti-synthetic ammo mods, I keep the best Armor Piercing/Tungsten rounds, about 3-6 each. Tungsten stops at level VII and there is no equivalent at later levels.
For other ammo mods, I keep a few Incendiary/Inferno, and Chemical/Polonium rounds (Polonium stops at level VII), about 3-6 each. I keep 1-2 of other ammo types like Cryo (stops at level VII) and Proton (stops at level VII) and High Explosive. I keep a few Hammerhead rounds until I get a few Sledgehammer. I sell all Snowblind rounds since they suck. High Explosive is only good on shotguns and sniper rifles. Keep one or two backups for yourself, sell whatever you do not equip on squadmates.
Basically for ammo, you want a bunch of anti-organic and anti-synthetic mods, and then a few specialty ammos for certain weapons or Krogan. You always want anti-organic/synthetic ammo for you and your two squadmates.
For armor, I always equip my squad with the best stuff you can find. Typically, the armor with the best damage protection is better for everyone. This means Colossus armor (starting at level VIII) is best for everyone. Some exceptions include Geth armor (Beserker/Rage) for Wrex; it has slightly less damage protection than Heavy Colossus but it has higher shields and tech/biotic protection. Predator L/H/M armor (starting at level VIII) has the best shields so you can wear that occasionally one some classes if you prefer. Also, Devlon Industries armor can reduce environmental hazard by 1 (can be worn by anyone in the squad, does not stack).
For biotic amps and omni tools, I equip my squad with the best available. the best are Savant (starting at level VIII), but can be rare. For amps, cooldown is most important, followed by duration. For omni tools, tech cooldown is typically best, although med recharge or shields is better on Liara. You may want to keep one spare omni tool or amp so you can swap between squadmates if you switch squadmates frequently and have only one or two good amps/tools.
For weapon mods, do not keep too many. Equip what you like or need on your main weapon(s), sell the rest. Scanners are not very good until you Combat Scanner X (when they are always guaranteed to cut through enemy jamming). But Heat Sink (up to level III) and Frictionless (starting at VIII) are valuable. The rest are up to you. I would never keep more than 3-4 of your most-used. Equip the rest on squadmates or sell.
For armor mods, anything with cooldown reduction or health regeneration is gold. Damage Protection is fine I guess, but cooldown and health regeneration is king. Medical Exoskeleton (starting at level VIII) provides both cooldown reduction and health regeneration so equip on all squadmates as you get the drops (Shepard takes priority) and sell everything else. If everyone has Medical Exoskeleton mods, sell all armor mods.
For grenades, you only have five mods: Incendiary, Cryo, High Explosive, Polonium, and Anti-Thorian. You only need the highest level of each, so five total (Anti-Thorian is only level I, the rest go up to X). If you never use grenades, sell them all.