As for the case fans in the front, I would consider buying one or two of these to go in the 92mm holes. Don't skimp on these fans as the smaller size of the 92mm can make some models VERY annoying. These noctuas ought to be silent, but you may have to hook up some speed controllers (or motherboard) to keep them tame. But I digress, I really do think you should put at least one fan in the front of the case, as push/pull configuration is far more efficient than a single fan in the back of the case. (even if your fan in the front is spinning very slow!)
As for the CPU cooler, I'm not too familiar with AMD sockets, however SPCR has reviewed many CPU coolers that are compatible, so check that out.
Do to your budget limitations let me suggest the following ideas:
Leave the tri-cool in the back, but pop it on lowest setting. Consider cutting out the back grill behind the fan to maximize airflow while still keeping this fan quiet.
For your hard drive, I would recommend getting a nice 1TB drive. For most users, they offer ample storage at pretty much an unbeatable price.
http://www.newegg.com/Product/Product.a ... 6822136534
If you really want to cut down noise at the expense of slightly longer transfer rates, check out the Caviar Green models and some of the lower RPM models from Seagate. Both are great options.
As for vents, other than the front 92mm fans I suggested and cutting out the back grill, I wouldn't do too much messing around with this case. It's already a great quiet PC platform, so I would leave it alone for the most part. I would probably block that side vent by the way...to me it's just a source of sound leak and doesn't offer much advantage unless you put a fan there. Block it off with some dense material followed by foam ideally.
