If you get a powerful enough laptop you don’t need an external GPU. At least right away. I would probably buy a beefy gaming computer. I’ve had a few MSIs and they’ve been great. They also have slimmer “stealth” models if you need to lug it around.
Putting an offspeed clip in a 24fps timeline doesn’t make it look like it’s been shot at 24fps although it is running in 24fps (frame drops or blending included).