The Discord server of the MKDS community offers a service which can send your submissions Discord too, in case you can't solve the issue. But yeah, good luck solving it out as the site is very old and has its problems due to that.

there has been a very long discussion about this, in short:

Pros of D-Pad:

• Very easy to learn.
• Easy to be consistent (not failing Mini-Turbos).
• Most used between the 2.
• Very slightly more precise.

Pros of C-Pad:

• A lot faster for making Mini-Turbos.
• Cold hands aren't a problem with C-Pad, unlike for D-Pad.

I'd always go with D-Pad no matter what the console is, as it allows you to get good very quickly. In GP Speedruns I find it a must since it would be the best to not fail any Mini-Turbo, and C-Pad is risky on that. C-Pad has the advantage of being fast, meaning that you will be able to PRB with difficult karts like ROB-BLS right after you get used to it.

As Cros said, it's more of a personal choice. One of the best players in the world uses C-Pad, Wazz who is between the best 150 uses C-Pad, all the rest uses D-Pad. As you can see, you can be very good with it, Taiga uses it and broke incredibly difficult World Records. So just choose whatever you want and have fun with it! You can always try both too, much like I occasionally do.

Sorry for late response, but no you can't (yet, at least). You can only use the 0.2 Version of the game.

just wait for bitter to start posting videos mirrored too, not just sidways 😏

That is going to take a while since no one really speedruns Grand Prix mode. But I'll try participating in breaking this, lol.