I need some advice: I'm currently working towards going after the Reaper IFF (I'm playing on medium difficulty), then to the Omega 4 Relay, but I'm spending the time upgrading everything and doing all the side missions. I already fully upgraded my ship with the armor, guns, and multicore shielding (so I won't lose anyone en route to the base, fully upgraded my assault rifle as well as partially upgraded all the other weapons; I've recruited all my crew except Legion, obviously, and have all their loyalty except for Jack, whom I sacrificed her loyalty for Miranda’s— after all, Miranda is hotter and my paragon/renegade points weren't high enough to keep both of them.
I am currently 3/5 with paragon, 1/5 renegade.
My current plan is to keep mining until I get 10,000 element zero, so I can afford the advanced training twice- once for AP bullets before I undertake the Overlord missions (there are a lot of synthetic enemies, I'm assuming, since I will be dealing with enemy VI), then before I go to the Reaper ship, I plan on switching to Shredder bullets, which will tear apart the husks and other biotic enemies. Or am I making a mistake switching to shredder ammunition?
Now that I think about it, the Husks are easy to mow down with my light machine gun anyhow with incendiary ammo, but the Scions are harder to kill. And the Scions are armored, so I think I’ll keep the AP ammunition. Gee, I think I just saved myself a lot of time scanning for element zero!
But what I'm asking is, once I get Legion to join my team and earn his loyalty, do I keep Tali’s loyalty or Legion’s? My paragon level isn’t good enough to keep both of them, I don’t think (how high does it have to be anyways?) I heard that Legion is more useful than Tali, but I’m not sure.
Also, how does the final mission work? What determines whether a squad member dies or not? Loyalty? In that case, I’d lose two members since everyone else is loyal, but is there anything else that comes into play?

On a side note, does anyone else think that the side missions, as well as some of the loyalty missions, are painfully short? I mean for Tali, her mission took me all of 15 minutes, and one particular side mission only took a grand total of 7 minutes. I am definitely playing this again on hard!

One more thing: I've heard how after you beat the game and if you survived, you can start over with all your upgrades still there (but not paragon/renegade points). Is that true? I would love to start the game with the fully upgraded LMG, but this time I'm going to be a renegade.