It's an interesting question about secret service and Trump in prison. I would assume he would be handed-off to corrections officials, and the secret service would stand down until such time as he is released.

...the next republican president will pardon Trump (even if, keeping this on topic, heaven forbid, it's Trump himself)

I don't think that will happen. He's too toxic. He can't win again because too many people will show up to oppose him (including some Republicans). And issuing a pardon (let's say DeSantis wins) doesn't really have any benefit. You appease a few hardcore Trumpies, and p-off practically everyone else. There's a reason most politicians are trying to distance themselves from him.

Way too early to call, but I'm not really seeing a Rep candidate that is exciting people. DeSantis was almost a shoe-in, and then he picked a fight with Disney. He's been floundering ever since. His own party is criticizing him for it, but he continues to double-down. I hear that Chris Christie is considering a run. He might actually get more support than DeSantis at this point. Not sure who else is in their stable right now.

With the economy improving, it's shaping up to be Biden in 2024. Lots of stuff could happen in the interim, so I'm not making a prediction. The QOP is a mess right now, and the economy is producing lots of jobs. If (big if) that continues, it doesn't look good for the Red Team.