HP - high pressure output (typically 850psi range)
MP - med (650)
LP - low (300?)
Your tank says it can be adjusted to all three ranges, with the marker operating at 225-300psi, you maybe able to use the LP setting. If you get velocity drop offs at higher rates of fire, try going to the MP setting.
As for a hopper I think the Invert TOO Halo was running for 50$ - good hopper for the cost, should keep up with no problem. (I personally have not used it, just off the top of my head a decent hopper in that range.)
That tank should work perfect. "The Shim design allows you to adjust from High, Medium, or Low Output Pressures. Change output pressure by adding or removing shims, not springs or pistons" - quoted from the site.
So you can adjust your tank to use LP. Then if you get velocity drops when firing at high rates, just adjust it to the MP.
Argueta, with a few exceptions (Trigger frame, eye(s), input regulator) your gun is identical to a Diablo Wrath. If you ever need in-depth support you might want to ask questions at the Diablo forum. People there are usually very helpful: http://www.pbnation.com/forumdisplay.php?f=332