And if folks would post specific questions, I'd be happy to offer specific answers.
Dies are going to be a PITA to get. I was lucky and got Redding to make a custom set.
Horneber brass is going to be the best brass you can buy for the chambering. It will be pricey at over $3 a piece, and you'll have potentially a 6+ month plus wait to get it. Jamison brass can definitely hold you over until you get the Horneber stuff though.
Powders will be H50BMG, US869, V570, Retumbo and RL33. Ramshot Mag and H1000 will work, but load density will be load and will velocity potential.
You'll need to anneal and SS media tumble and love on your brass and treat each piece as work of art...vs the Lapua or RUMs because the stuff is so much more readily available, it won't hurt so bad when you lose a primer pocket or lose a piece in the field.
You'll use 120+ grains of powder per charge, so that eats up time at the bench throwing huge charges, and empties out the powder cabinet pretty quick too.
You'll need to use Cheytac sized ammo cases for storage and field transport. Check your case trimmer and make sure it's got enough throw/travel to trim a case this big. Same on your press. It's a tight squeeze for a T7, better on the Ultramag press.
If you're going to build a gun with a barrel longer than 30" I say go for an Excalibur.
If you're going to build a gun with a barrel 28-30" I say build a Lapua IMP or RUM wildcat.
If you're going to build a gun with a barrel that's 26-28 go straight Lapua or RUM.
My 2 cents...for free!