i3 has a higher performance per clock than an FX proc but its just not something I like to recommend due to system overhead and other things that require being run such as firewalls/anti virus/anything extra you might have running in the background. Though I might be wrong on this and its mostly person preference as to whether grab an i3 or an FX proc at the same price level.
Motherboard: With an H61 you either are not going to be able to run an ivy proc or you would need a board with a bios capable of running them and hope its already updated when you get it as you can't run a bios update without a cpu in it.
I'd just drop the SSD, 64gb isn't able hold much at all and as you get down into those 64gb drives the price to performance ratio is really bad not to mention they don't perform THAT much better than a conventional hdd to make it worth it.
I'd try and pick up 2x4gb so you get the benefits of dual channel ram
Might think about dropping down to a lower priced card so you can pick up better parts overall (better mobo and cpu mostly)
No reason to grab a 670 and an i3 as in wow and BF3 (don't know about splinter cell) the i3 will bottleneck things pretty hard.
can i use an extenral drive 1TB and make it work only with a 64gb internal drive?
Uhm yes, you might have trouble installing games to the external, I've never tried that. But at worst you can just take the drive out of the enclosure and use it as an internal drive. If you do that you might need to get a 3.5 to 2.5 adapter depending on drive size.