Concerning screw length, it's not an issue. The routerbase for the DW611 has screw holes that go all the way through, except for two being covered by the plastic guard/dust port but I already drilled those two out so all four screw holes are now open. I only did this so I don't have to split hairs on measuring. Just get 3/4 or 1 inch. I wanted to get panhead so I could drill flat bottomed holes to guard against them pulling through, but I'll look to see what I can get. I might be overthinking it but I just figured a small screw like this would have a small head and this little router is fairly weighty for its size, not to mention this stand is going to see a lot of being bounced around. I had also thought maybe I'd route a recess into the bottom side of the top to elevate the router another 1/8 or so. I don't need to do that (see another thread I just made on this) but I had thought it would keep me from ever putting a bit in too deep and finding out after I've already put the motor back in the base that I have to take it out and start again. So the recess would help that but it also thins out the material between the base and the screwhead.
I've got 4 flat heads screws countersunk into a piece of 1/2" MDF. The screw heads are just below the surface of the MDF so as not to interfere with the workpiece. MDF is a real nice flat surface and I've put several coats of oil base polyurethane on it. Less expensive than a high quality piece of plywood. If it needs to be portable there are lots of plans for portable router tables...some will even break down for easy transport and storage.