The DrBud method goes as dense as 16 plants per square feet. It's all going to depend on the strains you grow and their structure to find what will suite the area best.
You can build your own carbon filter for pretty cheap, but if you just want to buy a cheap one I'd recommend the CAN 2600. The S&P TD100 would be a great fan for your setup. Do a little searching and you'll find plenty of good reviews about the S&Ps. They are relatively quiet compared to inlines, move enough air through filters, and take up very small space.
You can build your own carbon filter for pretty cheap, but if you just want to buy a cheap one I'd recommend the CAN 2600. The S&P TD100 would be a great fan for your setup. Do a little searching and you'll find plenty of good reviews about the S&Ps. They are relatively quiet compared to inlines, move enough air through filters, and take up very small space.