itch.io

I do agree with the first two points you make but about the third. When I've tried in the past to make controls for mobile automatically appear when on mobile it hasn't worked on the html version though I did do it slightly different where i made it check if the device is mobile or not. I probably am wrong though as I am quite new to gdevelop and you probably have more experience than me 

I am unable to change the speed of the box because it isn't a value, I can't tweak it

Well not yet. Instead I'm planning to update and improve this game after the game jam