I had a couple of models that I did as a kid and decided to redo. the paint was enamel and was all brush painted. Instead of trying to remove all the paint, I broke down the models as much as I could till I had a pile of large parts, small parts and clear parts.
I then did a light sanding with 600 grit sandpaper on all the larger parts. Once I was able to smooth out what I could see, I shot some primer on it and sanded any other blemishes I missed.
With all the issues fixed I primed once more and had a clean smooth surface to lay a new coat of paint down.
I soaked the clear and small parts in oven cleaner over night, wiped away the paint, polished the clear parts with 4000-8000 sand paper and dipped them in future. They were crystal clear and ready for paint.
For small parts like cockpit and landing gear, I wiped away the paint after the soak, shot primer on them and they were ready to go.
Prior to dismantling the models, I put them in the freezer over night which made the glue brittle. The models came apart much easier and I did not have to do as much cutting etc to get it broken down.