Re: new to shooting and the forum need advice.
Look up the Savage 10PC at
savagearms.com.
Unless you're going to be regularly shooting at well beyond 300yd, the .223 chambering will provide the ammunition availability you seek, while providing more economical choices. The savings could help you start and maintain your handloading capability more easily.
At your stage in the game, a custom rifle makes less sense than later; when your strengths and experience will provide you with a better grasp of where equipment improvements are actually needed.
Meanwhile, the custom budget might be better spent on a simple, reliable .22LR bolt action repeater. Your learning and training/practice needs are going to be far better served by such an implement.
Real tactical shooting, as you put it, is the sport of the physically fit. I know I'm not so fit, and suspect you're wondering about that too. All I can suggest about that is that you face your demons squarely, and listen to your body if it's not so willing to 'get with the program'.
Your path could go either way in this. Personally, I hope it goes deeper into the sport, and serves as a basis for upgrading your overall physical conditon.
But if it doesn't, that's no cause for disappointment.
When I found that I just wasn't ever going to become competitive on a physically biased tactical competition playing field, I never let it stop me from enjoying precision shooting. I simply turned, as many like me have, to F Class; which shoots the same distances with largely the same equipment, but puts less emphasis on physical prowess.
My path is my path, and nobody else's. It is governed by playing to my strengths. Seen from that viewpoint, anybody can enjoy the shooting sports.
Greg