The bigger the speaker, the more cone area. The more cone area, the more air that can be moved. A 10" will hit harder than an 8" in an ideal enclosure. Also, the more watts an amp puts out, the louder it gets. A 20k rms amp will destroy a 1200rms amp.
Sundown speakers last alot longer than walmart brands or entry level woofers, if you don't do something to mess it up.
Yea, you would need mdf. Depending on your space, you would be MUCH better off with a custom built box, which is simple to make. Normally pre-fab potted boxes are tuned too high and are not ideal enclosures for subs.