Does this come with seaweed sheets?

No. The gourmet grazer does not come with seaweed sheets.

I see reviews saying the magnet is strong but is it *too* strong that it is hard to move around or remove? 32 gallon tank.

Works well on my 65 gal tank with 3/8” glass. The magnet is not hard to remove when attached directly to the feeder itself so it should work fine on a 32 gal tank. My Tangs love it.

How strong is the magnetic. Will it hold threw 19 mm glass?

The magnet is very strong, my fish don't like it so I went back to the magnetic clip seaweed holder.

Has anyone used this to feed an urchin? I want to supplement my urchins with nori and trying to find the best way to go about it.

I am not sure about this, but I have tangs and put nori on clip and my urchins will find it and attach to the clip to eat it. I am sure if they happen to move onto it they will eat any nori. Good luck!