Obviously, all of this is my opinion...
DRDT-2 - I've used it, it's awesome. It's also bulky, heavy and mostly single function. I'm in a limited space shop and decided to stick with my C-Frame even though it's loud. Additionally, there's a Cleveland conversion kit that turns the C-Frame into a back rivet set. Likely not going back to the steel plate method unless I can't figure out how to make it work in some situation.
If you've got the space and the money, the DRDT-2 is probably worth it.
I have a NUMATX, it's amazing after you set it up. Come with several cups of patience on setup though.
You may want both a hand squeezer and a pneumatic variant. Hand squeezers are nicer / easier for one-off squeezing and "fattening" replacement rivets (not sure what the official verbiage is here). If you have a row of rivets to run though, the pneumatics shine here. This is especially true of the NUMATX which for all intents and purposes has 2 settings - one for 3/32 rivets and one for 1/8 rivets. Setup a single purpose regulator/gauge for it, figure out those 2 settings, mark them on the dial face, and you're done. I've also used a standard pneumatic, and it's not really much more effort to use. I'm just lazy.
Cleveland has an AEX wedge trailing edge squeezer set that's "expensive" for a single purpose item, but makes trailing edge rivet work Easy button work. Since you partially set the rivets on the first go, this is also where a hand squeezer is the go to tool (IMO). Final set can be done with a pneumatic.
I have a Sioux drill and love it. I've also done a ton of airplane part drilling with a battery operated Dewalt drill, straight off the Home Depot Aviation Supply aisle. The pneumatic drills are super light, so for extended use they are nicer to use. Also, the pneumatic has higher speed so for fresh hole drilling (vs. pre-punched) it's better, especially through thicker aluminum. If you had your heart set on Sioux, I don't see a reason why you couldn't get started with a normal drill until it came in stock.
I have a 2x (Sioux) and 3x (Avery) gun. I use and like both.
Tungsten bucking bar - just get it.
I do most of my shopping with Cleveland now, and have no experience with Isham. Cleveland has always given me excellent service.
Other nice to haves:
- Belt / Disk sander - I didn't see the point of having something like this for an airplane project. I was wrong. This is also one of those items where there are several variants and personal preferences really come into play.
- 10" Drill press - I try to do all my countersinking with this.
- 10" band saw with a metal cutting blade.
Both the belt/disc sander and band saw have eaten parts, so get familiar with those tools on something other than your project. This is a good rule, in general, anyway.