Flee2321 Please see this guide, specifically the part about moving the user folder:
📓[GUIDE] [PC] Choosing where Sims 4 data is stored | EA Forums - 12598500
As for what drive to buy, try to find an SSD (solid state drive), even if it's smaller than an HDD at the same price. The faster loading times will be worth losing some extra storage. And check reviews that actually tested the drive (rather than simply listing the specs) to make sure it's as fast as advertised.
Other than that, you can buy what you like from a company you've heard of. It's not difficult or expensive to make a good-enough SSD these days, which means quality options are plentiful and not that expensive.
