1) Accuracy isn't really going to be determined by the marker. Your #1 determiner in accuracy is the paint you use. Marker has actually VERY little to do with this. It can affect CONSISTENCY, but single shot accuracy no.
2) Just about any quality marker if properly cared for will do this. I never have to work on my markers at the field if I haven't been adjusting them before playing.
3) If you're willing to buy older markers (I'm guessing you are since this is mcarterbrown...), then price shouldn't be too bad. You can pick up nice older mechs for <$200, and nice older electros sometimes too. Worst, older nice electros will run you still <$400 unless you want something really rare.
4) Get anything past ~03 and it'll be light (ish). There are exceptions, but that's a decent generalization.
5) Just about any mech and some electros fit this bill great.
6) I personally love recommending Quests. A bit older, but fairly light, very nice looking, quick, and can be had for ~$200. But doesn't fit your desire for co2. So I'd recommend either a used slide frame cocker (just feels better) or a mag. Both quite quick enough, can be used on co2, and insane reliability once they're set up correctly.