Your still doing good. No, you don't need a manifold. You need 2 valves per corner. One to allow air in the bag from the tank, and one to let air out. Some valves are mounted on a block (or manifold) but that isn't required.
The York compressor is the way to go if you want a lot of air in a short period. The are very reliable, and quit too. The down side is, the are large and require brackets that can get complicated. It appears you already understand all that though.
It is more common to run an electric compressor. They are "fairly" cheap (start at $100), and easy to mount. They are noisy though. One of the more popular brands right now is ViAir. They are good compressors, but the are loud. The most common is the Thompson 315 or 317. They will do the job just fine, but none of these will compare to the York in speed.
How are we doing so far...
