A couple of things. find a source of Baltic Birch plywood and pick the flattest piece you can find in 3/4 (18mm). Some wood supply stores carry it. Keeping the table flat over time requires a little work. Either add a second layer of MDF, or put some straight 1x2 or 3 trusses underneath. Or do both.
Cutting the opening for the router plate requires a template and trim bit. I used the router plate itself as a guide, then snugged four pieces of straight 1x up against the plate, with maybe a playing card between plate and board so you have a nice fit, but not too tight. Clamp the boards in place and you have a template. Drawing attached. Using a trim style bit with a bottom bearing to follow the template. Set the depth a couple of millimeters/ 16th to 1/8 th deeper than the thickness of the plate. Use your plunge base, or the fixed base to create the rabbit or ridge on which the plate rests. Pictured are some plate levelers you put in the corners to line the plate up with the top.
I prefer an aluminum plate, stronger and flat, don't sag. There are all kinds of fence designs, but they can be pretty simple. Rockler makes a little dust hood that boes behind the opening in the fence. So far we're up to about $60-$70 bucks. You already know how to build boxes, so make one into a stand for your top if you want.
Keep it simple, but precise.
The leverers are Woodhaven. The bit is like what you're looking fo.
The more I do, the less I accomplish.