I agree with everything said here.
Ultimatum makes some very "interesting" design decisions on their actions, which confuses me as a consumer of precision rifles. If you don't understand the nuances of the Ultimatum actions, I can see it resulting in a pretty frustrating first time custom rifle build. In fact, I know someone that went through that with Ultimatum, and it was a very frustrating experience for them. They went back to Savage rifles
I would look at Bighorn Origin, Kelbly Atlas Tactical, or Defiance Tenacity for very well made actions that come in at a good price point. All these actions are held to tight enough tolerances that shouldered prefit barrels are available, making rifle assembly a breeze. All are Rem 700 footprints, accepting R700 aftermarket components.
The KRG Bravo is an excellent chassis at a budget price point. Lots of accessories available for it, so you can really dress it up as needed. If you want to spend more, they have other options as well. Hard to go wrong with KRG, good choice there.
For muzzle brakes, I would look to any of the self-timing brakes that are currently out there. Insite Arms Heathen, APA lil bastard, PVA jetblast, Area 419, etc. Personally, I've had most of them, and the Insite Arms is my favorite. In my opinion, it's the most refined design of them all, but they all do a good job of mitigating recoil.
For optics, give Doug (
@gr8fuldoug) at CameraLand NY a call. He'll have a few options in that price point.