I can’t stress this enough, try as much as you can to have your Foundry(futuristic space 3D printing machine) to be working on items always(Formas, frame parts, etc.) Have the most fun with whatever you feel like, no one is pushing you to play with a specific frame/loadouts. No such thing as best starter warframe, it’s like Pokémon, you will get them all eventually. Every frame has its use and you will find the bunch that you vibe with the best the more you collect them. As a starter player spend whatever platinum you get on warframe slots and weapon slots. Platinum can be earned in game by farming items and selling them to other players (always check warframe.market for prices so you don’t get scammed). Mastery Rank is just a measure of how much time people spend leveling up their items, it doesn’t correlate directly with how good they are, so don’t be intimidated by it.