Should be, yeah. The revised core rulebook was pretty much complete in itself, if you ask me. All the various supplements that came out were just supplements.
The aliens book is nice to have, but really, I've found that virtually all of the PCs in my groups that I've run have either played humans exclusively, or have had the very occasional odd-ball species.
As I understand it, there will be RCR-->Saga conversion rules made available online, so I doubt all the current supplements will become obsolete. Obsolescent maybe, but not obsolete.
Saga sounds a bit more complete than previous editions with the inclusion of a Universe Guide. I'm assuming that will give some condensed details of planets and such.
To answer the question...yes, the core book will be all you will need to play (and dice).
BUT, the SW universe is huge and you will probably find yourself wanting a bit more information in some areas, either essential guides, novels, or old D6 or D20 supplements. Of course, you can get a lot of small questions answered simply by asking on forums like this one.