Keychron has some good entry points for getting into the mechanical keyboard scene. Lots of layout options, some open source keyboard firmware support, and you can buy a lot of them barebones if you want to bring your own keys and caps.

The couple I have built are mostly built by myself with some outside suggestions from a friend. Usually you are safe to browse anything so long as you can find some legitimate user reviews (Video reviews preferably) - pre-orders, and especially group buys can be risky. This goes for parts as well as full boards. It's also good to look into whether the seller has good documentation/a build guide if the keyboard does nifty things that are not very standard. I just got a QwertyKeys QK101 which I finished building last night - I can verify that they as a seller were really quite fast as far as delivery goes, and the board is working quite nicely, has some really neat magnetic connections inside that connects the battery to the PCB and the PCB to the screen which made that really easy. Also hot swappable for the switches, so I didnt have solder anything. Have also heard pretty good things about their other boards. For switches I use a seller called RNDKBD, and for caps I usually look at DeskHero or CanonKeys.

I made a post with a picture and part list you can see on my profile.