General:

F-zero GX is an extremely hard game to speedrun and takes a lot of practice until you can get a good run. Patience and time to practice is extremely important if you want to set good times for this game.

There is not any major version difference known yet regarding gameplay. You can speedrun this game on every single version of this game. The only difference between versions is languages and that you die on the japanese version if you don't make ch. 5 in 40 secs ( this is a very minor difference ).

getting really started:

Here is a list of (almost) all advanced techniques (AT) in this game with a brief explanation: http://fzerocentral.org/viewtopic.php?t=463

The most popular category is maxspeed, hence all categories on the leaderboards are max speed so far, which means some tricks are not really required to learn like spaceflying or snaking.

A good way to get into this game is beating it without any ATs to get a feel for it, but this can be very frustrating. Whenever you want to start learning ATs, then I recommend following this guide by Vallkyr: http://www.fzerocentral.org/viewtopic.php?t=13780 and learn the most important ATs individually from the easiest to the hardest.

While learning the most important ATs, you can start doing time attack. You will not get a good time on any category without time attacking, the more you play the more your skills improve and time attack or time attack practice is the best way to improve.

You can find some good and rather easy strats for each track on this tutorial playlist by Naegleria: https://www.youtube.com/playlist?list=PL5UD8kOhQuv8I3IpEU57N1pCAeiYQNr36 However I recommend to try out different vehicles and strats yourself too and maybe use a different vehicle than suggested, because you feel more comfortable with it, but if you want to go for better times your vehicle choice will be more and more restricted. Doing research on your own is always good.

Try to improve on each track and get a time you are satisfied with the strat. If you think you need to add harder strats to improve, you can find many strats from other GX players. Here is a list of playlists where you can learn strats from: http://fzerocentral.org/viewtopic.php?p=100364&highlight=#100364 ( and there is still a lot more )

I also recommend to join the F-zero GX discord channel where you can find many other active GX players, that can give you advice: https://discord.gg/0SjuQvhyEztYYVno