What games, say from B/W1 onward, could I combine to get the most possible Pokemon?

I'm about to go on deployment dat navy life though, so I'm going to be unable to trade with anyone online -- just other people on my ship. Right now the OR/AS dichotomy is handled because there's a dude in the same berthing as me with AS where I have OR, so no worries there. And I already had Y. But, between X/Y and OR/AS, would I be able to get all Pokemon possible? Do I need to add B/W, or B/W2, or both, or neither? Are there any left over in DPP, or maybe HGSS, or even FRLG, that somehow never made it into the 3DS/DSi games? Basically, how far back in the series do I need to go to be able to capture all my own Pokemon (with the exception of trades from AS/X, not being either of those because they're both still too new and, thus, expensive)?