Quite tricky to play this one. The first section is made up of campanella bits on G and Am (5450) mixed with short runs. For the runs in both sections it’s worth using pinkie, ring and middle for fretting. It’s a stretch in some places much makes it easier to set up for the chords.
My picking in this video is, I’ll admit, a mess. I use my thumb, index and middle and move them between strings. It’d be better to allocate one finger to each string in the campanella parts. Also, I used just my middle finger to pick the runs. It’d make it easier to speed up if you used index, middle, index in a running-man motion.