Stock pistons are fine but if you are going to take them out you might aswell notch them to be safe , or buy some cheap RS machines
If your going to keep the stock pistons then make sure you get the B20B8 with PHK written on the intake manifold cover, due to the better compression ratio
Everything seems to be right except you forgot breather kit. Computer there are many options, i would go for a hondata s200 pretty cheap these days.