1-Is there a set of standard gerber files ?
No...yes...kind of. It's common for Eagle users to generate:
.cmp: top-side copper ("component" side, hence cmp)
.sol: bottom-side copper ('solder" side, hence sol)
.plc: top-side silkscreen (PLacement on Component side)
.pls: bottom-side silkscreen (PLacement on Solder side)
But there is no standard for what the files are called. Just be clear about it when you submit your files.
2-How do you review and verify your files before submitting them ?
Use a Gerber file viewer like GC-Prevue, ViewMate, or gerbv for Linux/Mac systems.
3-Is someone out there accepting Eagle files ? (In case this makes sense)
Yes...but don't do it. You are counting on someone else interpreting your board and generating what they think is the CAM data. Proceed as you suggest above: learn to generate the CAM data, verify it (twice) using a Gerber viewer, then submit that. You will have much fewer surprises.
The Gadget Shield
: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons