It is a foolish idea. A Speaker does not need to be a member of the House. Only 14 RAT senators are up for election in 2022. The math does not work.
Sentences #2-4 don't have anything to do with sentence #1 (unless the "idea" is something other than Trump serving as Speaker).
What is important is that Trump become active once again in the government if only to grasp a better idea of how D.C. works. He would likely be the first to admit he listened to many of the wrong people that found their way into his administration, or even those he believed he could trust. Doing that few years of additional work will make him even more capable after regaining the WH in 2024.