Don't forget about workholding and toolholders are Cory mentioned. Those are the big expenses up front. Bare minimum you want a step block kit and 1 or 2 good vises. Kurt is the standard, but we have two Glacern 615's (
http://www.glacern.com/gpv_615) that have been great. About half the cost of the comparable Kurt (3600V), it gives you the ability to clamp the vise on it's side for tall parts. Jaw bolt pattern is the same as the Kurt's, so you can use any of the industry standard step jaws, v-jaws, soft jaws, etc.
Are you set for CAM software? That's the other big consideration for most teams. We use EdgeCAM since we use it in our PLTW classes, but MasterCAM is probably the most widely used package.
I don't see much use for any end mills over 1/2" - it puts a big load on the pull stud, and the TM machines don't have a ton of torque/HP to start with. Power output drops off at high spindle speeds you'll be using for aluminum. There are motor curve charts out there if you do a little googling. Peak torque for the TM-2 is at 1200RPM as per the Haas site. For frame rails, gearbox plates, and the like, there's really not a lot of need for a huge end mill.
Form taps are good for small threads (#4 & #6), but for bigger sizes I've never seen a big advantage. Spiral point taps (shoot the chips ahead of the tap) for through holes, spiral flute taps pull the chips up and out the flutes of the tap (for blind holes). Buy a bunch of the appropriate wire gauge pilot drills (#36,29,21,7) in short or stub length. We buy the "Heat-Resistant Cobalt Steel Short-Length Drill Bits" from McMaster (28765A57), Cobalt is unnecessary, but McMaster only has TiN and Black Oxide in short length HSS, and those are both bad for aluminum.
Get a mill/drill with a 90 degree tip. McMaster stocks those as well. They can do triple duty (drilling, spotting, and chamfering).