Does anyone know how to use ceramic tile on a countertop? Do I remove the old countertop completely (there is laminate on it now). The countertop is very solid. I am planning to use Schluter membrane on top but was thinking that maybe I should be installing a plywood first.

Any suggestions?

Yes, you need to remove the laminate counter top.
Have a look at this article. http://www.schluter.com/media/articles/chw_art_countertopinstall_ca.pdf

Also give some thought to using epoxy grout to make it safe as a food preparation area.

Chuck, is this you?