There are a bunch of different factories making these kinds of motors, and their parts are generally interchangeable. If you're talking about "performance" parts for an HT, it's going to be intake and exhaust, and those are definitely interchangeable.
But you're not going to put "performance" parts on it from the getgo, except maybe a spark plug. You're going to put it together and ride it a bit, then add bits and pieces later on. First build, make it stock. These motors do run just fine out of the box.
Don't go crazy tearing things down that don't need to be torn down. I know a lot of people like to do a little port polishing, that's not going to hurt anything. But the carb is so simple, there's really nothing to do to it, apart from setting the throttle needle. Besides that, the HTs take a little while to break in, so wait until you've got a couple hundred miles or so to tweak. And the carbs are overjetted anyway; they're about guaranteed to four stroke on 32:1.
Electrical is a sealed CDI and a magneto. The mags tend towards being fragile. Leave it alone unless it demands your attention.
The in-frame engine mounts flush to the seat tube, and then whatever you have to do in the front to make it rock solid there. Failure to mount to the seat tube flush and solid in the front will result in broken studs at best, broken engine case or frame at worst. Yes, you can put it on a bike with a front derailleur, but the engine may have to be mounted higher on the seat tube, requiring some inventive front mount fabrication. Or at least a bunch of washers as shims. If you keep the front derailleur, you'll have to be creative about how you handle placing the shifter for it, too.
Word is that the slant heads provide better compression than the straight heads, but the difference is going to be minor.
Best advice I can give you is to repeat what I've said. Focus on proper engine mounting, proper sprocket mounting, and chain clearance/tension. Don't get focused on electrical and carburetor, because those are secondary problems, if they're even problems at all. Get it put together right the first time, get it running (even if it's not running top notch) and break it in a little bit.