Is a running start possible in Adventure DX? By running start, I mean like in recent games where Sonic is already running at the start of the level. I don't know whether editing the exe in SADXTweaker would do the trick by changing Sonic's action at the beginning of a stage (standing by default) and I don't want running starts for the HUB world either.

You could just simply put a Dashpad where Sonic starts

Yes, that could work, but it'd have to be invisible, plus with no sound, and sadly that might require a new slot, which we don't (yet) have the ability to create. Ah, well. I'll look into the matter a bit further.