My approach for the main series would be to examine the successes and failures of previous games and use that information to refine the gameplay. 2D sections wouldn't be eliminated entirely, but would be a much more secondary gameplay style compared to the 3D. I'd also bring back multiple playable characters, using it as an opportunity to include other alternate gameplay styles but make it so the only one you actually have to play as is Sonic himself. I'd probably go with primarily Frontiers style for Sonic, Unleashed/Generations style Boost for Blaze, Adventure style for Shadow, and several others. I'd probably avoid using Wisps for the most part, though I'm not against making them the exclusive gimmick of Whisper. I'd probably rather give her her own spinoff though, and make it sort of a 3D platformer Metroidvania in which she has to rescue each of her Wisp friends and use their powers to explore where she couldn't reach before.
I'd absolutely relegate a secondary team to making sub-series games focused on alternative protagonists. Their job would be to develop individual titles for the likes of Tails, Knuckles, Amy, Cream, Team Dark, etc, In particular, I'd like to see a reoccuring sub-series of games focused on Blaze as the main protagonist with Advance/Rush series style 2D gameplay. I'd probably also want a Shadow the Hedgehog 2, though I'd tone down the edginess and ramp up the air of mystery instead. Rather than being about Shadow's past, it would be about him working as a G.U.N. agent with Rouge and Omega, taking on a mission to look into some strange occurrences and get to the bottom of what's causing them and why.
Finally, I'd continue the trend of allowing talented fans such as STEALTH and Headcannon to make 2D Classic Sonic games taking place in the split timeline Mania is part of.
There'd have to be a strict policy against Crunch Culture in general. I'd also generally avoid announcing games until they have actually had the time necessary to be ready to show off so that reasonable deadlines can be set and delays can happen when necessary. I'm against the idea of teasing a game that is still years down the pipeline with little to no word inbetween until much closer to release.