Your question/s have many lengthy answers. But I'll do my best. when looking at SAP realize the TCO of maintaining the system. If you are a small sub group of a larger corporate structure there will likely be many legacy systems to roll into the B1 instance or up to the ECC SAP landscape of corporate. Things to think about, you will not just simply cut over to SAP, this takes at least a year and anywhere from a few good consultants to a small army. B1 and SAP are amazing tools with a strong future so ROI over 5-10 years is favorable. GP is similar to B1 so cut over training is not as bad as you think.

I myself have a Java .NET background from my university but ABAP is just another COBOL ish language. I won't go deep into ABAP/4 but its the primary syntax of SAP. newer features are possible in JAVA and you can install a Java stack in SAP. As far as what can SAP do? fuck man, it can run oil rigs, banks, car factories, charity orgs, just about anything you can think of.

I would suggest you start reading business cases and call an SAP rep to come in and discuss options. Of course we are SAP bias here but that's only because its our career!