Medium or low pressure are a bit better for internal air lines. The slp tank will get a few more shots. But nobody is having troubles with any tank they are tossing on. You can open most regs and add/remove washers and shims to change pressure.
Tires are free at the dump in a lot of places. You can make quite an amazing field with a couple hundred tires. Just place bottom row of bunker, fill them with dirt, pound the tire sides a with rubber hammer for compression, then place the next row.....
Not really movable once your done so get it right the first time.
How much would a used DM11 put me back? Cause I know a buddy selling a LNIB DM12 for 700$ but i dont have that much cash or I would of picked it up...
DM 9-13 will all shoot pretty close. The 9 or 10 will be $350-400 and great choices of you want a Dye or just a spool valve gun. DMs change very little from year to year. That said there are a ton of choices in this used market $500 range.
You seem to want, used super gun, single tube, low maintenance (cause you are new), reliable and good ergonomics. With that in mind, I'd advise; Eclipse Geo 1 or 2, Mac Dev Clone or Clone VX, Bob Long Victory, or DM 9-11.
These are all solid choices, all have their pros and cons. I'd take this info to the vs forum and do a little research. Good luck.