So, lots to choose from, what have I used and what do others say about these companies

CompanyAboutMy Take
GotohMaybe considered the best of the aftermarket parts providers
GuykerEconomy parts, but also have a “professional” lineI used their “pro” line of locking tuners and a floating tremolo on #1 and I am very happy with them.
MusiclillyEconomy parts, but also have a “professional” lineI used their pre-loaded Strat pick guard on #1. The pickups sound fine, probably better than the ones that came with the kit. It does have full sized pots (though probably not CTS). My only complaint is the thinness of the pick guard itself.
KaishPretty sure this is a chinese company, their “official” page is on aliexpress.I use some of their fret tools. I like my StewMac and Music Nomad tools, but they can be expensive. The wooden Radius Fret Leveler blocks are nice. The multi-angle fret file seems well constructed.

I have also used their locking tuning pegs on my #2. Seem very similar to the Guykers on #1