I know two other producers with years(sssssss) of experience that also share Rob's preference towards MAC's for audio production. I can't argue. I just hate Apple. Even my Surface Pro CAN'T hold a candle to my custom-built desktop...
But that said, they would all tell you to buy a Mac. 16 Gig minimum for RAM, 32 Gig would make life easier by a LARGE amount, 64 Gig would make you do a happy dance. The moral? Never skimp on RAM.
I would say build a mini-tower with 64 Gig of RAM, ASUS motherboard, and special M.2 lightning quick hard drives that are are the next gen of SSD (with something-like over 300 Mbps transfer rate), and the fastest processor you can afford. But, I'm super biased... and I'm not giving up my PC games.