In re limits: Don't limit by target platform. Sonic 3D Blast Saturn was just Sonic 3D Blast Genesis with a few touch-ups (fog and rain in Rusty Ruin, for example) and fully 3D special stages. Here is my stance on limitations: DON'T LIMIT ANYTHING YET!!! Sonic 2 had many innovations that Sonic 1 didn't have: corkscrew loops, most of Metropolis Zone, etc. Sonic 3 (alone) RAN with the new ideas: the hand-launchers, horizontally-crushing walls, and fans in in Hydrocity, the spinning tops in Marble Garden, most of Carnival Night, the lifts in IceCap, etc. The Death Egg Zone in Sonic & Knuckles should be enough to make you get the point, but there are also little things in every level (like the unique loops in Mushroom Hill, the sand falling from a tube in Sandopolis Act 2, etc.). There wasn't a lot of limitations to the ideas initially; if there was, I doubt any of that was possible. Let all the ideas come through. At one point, LATE in the game's development but BEFORE level maps are finalized, stop accepting ideas and reject the ones that may not work.