I like your choice of calibre, and the last rifle Im hoping to build for myself will either be a std 250, or a 250 AI. No need for justification, wanting is all the reason you need. For me personally I would like something like the Rem Model 7 action, or, if I can find one, an 1960's BSA regent action. A #2 contour barrel [I think], and fitted to either a high end carbon fibre classic style stock, or a simple classy walnut stock. I will have the barrel and action Ceracoated in a matt "blue" colour so it looks like an old school matt bluing job. And top it all off with a Kahle's 1.5-6 scope. I would recommend some research in to barrel twist, standard 25 cal twist rate is 1 in 10, maybe 1 in 9 would suit the heaviest projectiles.
And see if you can find a gunsmith that explains the actions and consequences for each and every part of the build. Like is 1-9 gonna be better, if so how far out do you want to seat the projectile, which will require x amount of room in the mag, does your action choice have that length of mag, or will it require a custom mag. Each choice you make will have something that needs to be considered. Is there a stock of your choice with the appropriate inletting for your action choice? Choose a gunsmith thats happy to help you with all the alternative components and who wants to enjoy the build as much as you do.