for scopes, i recommend one of these. my particular scope, a long-eye relief model, has served me very well so far:
canadian site too.
As for your other questions. I have heard many a time, even by people who love CA, that TM makes a better AUG. Basically, w.e you can get for cheaper, get it. In terms of of out of the box reliability, TM, hands down.
It is NOT recommended that you upgrade right away. Play with your gun for at least a year. Then upgrade.
To upgrade your gun to 400fps isn't necessary. Not off the batt. Once you are ready to upgrade, dont have to go to 400fps. At 380fps using .28g bbs, you will have the same accuracy as using 400fps with .3g bbs.
In terms of upgrades this is what i would recommend (but only down the road once you save up a pretty penny).
Prometheus 6.03 tightbore
Prometheus V.3 Spring guide
Prometheus Hard Piston
Prometheus Air Nozzle
Prometheus 110 spring (maybe a 120)
ARS V.3 Aluminum Cylinder Head w/ attached sorbo
ARS POM piston
Prometheus Soft Hop-up rubber (though through research, others would recommend Guarder Clear or Black Rubbers)
SCS (Shredder Concave Spacer) --> talk to amos to get these
Prometheus Torque-up gears
A decent battery from this site:
They make great stuff and my battery, along with my motor gives me instant trigger response. Honestly, a battery from this place is not so much of an upgrade as it is a necessity in my book. Again, it doesn't have to be from this site, but a decent battery in general is a definite must for airsoft. Also, with a decent battery, get a decent charger. Such as those TLP or Pirana ones.
Hope that helps!