Older Arduino Mega 2560 Revisions still ok?

Thanks for the reply!

I have read that R3 uses the 16u2 instead of the 8u2 for usb interface, does that make any kind of difference?

As for the shields there is one with LCD-Keypad, breadboard some wires etc. This would be useful to me.

I am seeing a lot of those Sensor-Shields. I dont really get those imho. Do they just provide better connectors for the pins or is there something else going on?
Are there things you would recommend as a must have for a beginner, even if i might not need them in my project (i.e. for learning) ?

Sorry for the dumb questions but i am really new to this whole uC world.

EDIT: I just realised that SainSmart is a company that builds boards almost identical to the Arduino but its not the original. That would explain the much lower price. I want to support the original project and developers however so i guess i will go with the original albeit the higher price.