If you don't have an AR sitting around, go for the full rifle. The $1k higher price over the receiver set is peanuts. There is a thread what you have to buy (basically everything) and you will end up at well over $3K. You can always improve the rifle at a later stage if you really like it and want to keep it. As to magazines, I would just cut the magazines in half for now and put a nice baseplate on it, maybe even change the mag release but that's what I would do for now.
https://www.canadiangunnutz.com/for...inder-technical-info-questions-go-to.2483222/
I am in the waiting stage for now since a few new rifles haven't been released yet, most noticeable the MK3, it does not have the rear charging handle but the Crypto also does not have the FA (forward assist). Depends what you want. If you look at the PCC (pistol caliber carbine), people really find the rear charging handle on the FX9 very appealing and it keeps the used price market and demand high. So for a newbie like you, buying a full rifle Crypto and doing small and slow improvements is probably the way to go. Cheers.