OK
A good electric airsoft would be a SRC Gen. 2 or 3 XM8..
Yes, it is AEG proline which means it is a fully automatic electronic competition level airsoft.
Not bad
AEG? Systema
8.4V NiMH 1400 mAh Mini airsoft battery See related links for a picture of the recommended battery.
You will find many decent airsoft pistols for ~$50 but nothing more. Don't buy an AEG under $140 or so.
The Jing Gong AK-47 or M16A1 are good AEG's that seem to be reliable.
Crossman Uzi
Springs in airsoft are never "modded" they are upgraded. An overall good brand for springs is guarder. Their springs usually run from $15 to $35 dollars. Madbull makes decent AEG springs for the money if you sniper takes an AEG spring (like the A&K SVD).
The g&g gr16 is a good AEG for its price. It is reliable, and an all around balanced gun.
You will lose velocity
The answer depends on if you are using .2 gramm or other ammunition, but yes that is the average fps for a moderate airsoft gun.