Yes, I think there is a chance that ultimately he will end up with a very very mild cp diagnosis, purely because of the fist/tremor issues - I don't think the rest of the gross/ fine milestones are in any way behind, so impossible to tell.
To give you some perspective, at the same age as your ds, dd2 could not do a darned thing. She failed every miserable milestone dramatically and continuously, was tight, spent her time with her hands held in fists, thumb in palm, tucked under her chin, and was pretty much unbend able.
She was not diagnosed until she was two years old, so I think you are going to have be extremely patient. The only thing of concern from your list IMO is the fist/ tremor. The rest seems unremarkable.
It is obviously a worry (dd2 was born term with a fhr of 28bpm, no attempt to breathe, ventilated etc. 5 weeks scbu - at 9lbs she looked like a sham- on oxygen, no suck, gag or swallow reflex) but babies are remarkably resilient. We were told she would not walk or talk. She is 9 now, and has an iq of 142, goes to ms school, skis, walks, runs, goes to brownies, is really a regular 9yo.
She still has cp though. It seems like the scariest thing in the world, but the brain is amazing. Your wee man will be busily building new pathways, and working out better patterns of movement etc. early intervention is key.
An MRI may or may not show brain damage. But without any clinical signs of cp, they are unlikely to bother to MRI. I am betting he had one during the three weeks he was on scbu, tbh.
Who does your outpatients clinic? They will be monitoring and referring on as necessary. Are you being reviewed six monthly? Or less? It's all you need at the moment.
If he starts missing milestones, ask paed for referral to physio.
He sounds as though he's doing really well! Just keep an eye.