Welcome!
RS Prop Masters is a solid choice, but I’d suggest getting in touch with the 70th Explorers Garrison before ordering, since they can help you avoid common approval and fitting issues with the armor.
Denuo Novo ready-to-wear First Order armour can still need adjustments, as it’s made for a specific body type. For 501st approval, many troopers prefer a trim-yourself kit so they can get a better fit and meet CRL standards.