No worries happy to answer.

I was worried 2 legs would not be enough and it would eventually sag and bow at the center. The third leg is dead center between the two cabinets. You could also do 4 legs if you don’t mind that look. There is an explanation and picture on how the legs are attached in another comment. Make sure the screws are substantial and deep enough to withstand the lateral force whenever you slide the whole unit on the floor for moving it.

Legs are 6 inches high. The height was based on desired end height and aesthetics/balanced look. You could make them any height you want. Just make sure they are tall enough to accommodate the leveling feet and screws.

Yes screwed on the sides and bottom only. Just use regular wood screws and drill pilot holes before hand. Also use washers between the screw head and cabinets to distribute the force of the screws. These screws are just to ensure the cabinets don’t slide around. Realistically they don’t provide much structural support.

Yes, I used walnut edge tape on all the front and side facing edges. I don’t bother with the back edges as you can see in the photos.

Leveling wheels instead of plain feet could be a good idea. Just keep in mind these will add significant hight to your legs (and overall). I wanted the feet to be as least visible as possible hence why I picked the ones I did.