Pretty good rig, dont see anything wrong with it.
If you can afford it, upgrade the SSD to a performance unit (the Agility is mid-range, more budget oriented), go for the Samsung 830 or OCZ Vertex 4. Though if you have to drop to 64GB to achieve this then stick with the Agility.
Should I hold off on the 500gb until after the holidays then because I already have a hard drive in my current computer. It's a "Seagate ST3640623AS ATA Device (640GB)" Figured it was worth an upgrade since this computer is a few years old and I bought it prebuilt.
If you already have a drive that suits your needs then use that. The performance of the HDD isnt really a factor now that everything important is on the SSD, just use it as a storage drive for your music, files and games (games receive no benefit to SSD's, so put em on the HDD).