Put the countertop on the base, put the MDF on top of the countertop, and line up the marks you drew on each end of the MDF with the countertop below it. When you have it lined up, clamp things down, and route the edge of the MDF using a 1-1/2" or longer flush-trim bit, with the depth adjusted so the bearing rides on the countertop. I clamped a couple of scraps of doubled MDF at each end to give the router base something extra to ride on at the ends.
Not sure about Midwest but I have a 24 x 14 Game rm attached to my shop and I put a small window unit/heat pump in the wall. It stays comfortable all year round. It get really hot here and we had a several day in the 20's this winter but it's insulated well. That might not be as cold or as hot as in some places but the unit I haze does not run that often and has a low cost rating. I'm planning on putting a larger unit in the shop area even though I do like to work with the garage door open. The door is insulated so I can run A/c in there. Just my .02.
This place is great! They offer safety classes before you sign up for a membership, and the workspace is big and well maintained. I needed some basic lessons with table and band saws, which went great. I didn't ultimately get a membership because my sawing needs are very specific, and ended up getting a small bandsaw for myself at home. But if you're someone who needs the whole range of tools, this is the place to be!
My advice? Don't do this. If you have jointer and a planer, use them. If you don't, seriously consider using dimensional lumber that has already been planed and sanded. If you are going to try to clean up construction lumber by hand, using a hand plane is a lot faster and more pleasant than using a belt sander. Except, of course, that to do a good job of planing a board you need a solid bench to hold the board, and you don't have a bench, yet.
Cut 15 top boards 5 ft. long and rip them to 3 in. wide with a table saw so the top will glue up flat without the typical rounded edges of 2x4s. For the leg slot, cut two of the top boards into three pieces: a 39-in. middle piece and two 7-in. end pieces. Glue and screw the top together, one board at a time, with 3-in. deck screws, keeping the ripped edge facing up and level with the adjoining boards. Use a corded drill so there’s plenty of oomph to drive each screw below the surface. Note that the third glue-up from each end is where each leg notch is inserted. You can also create a nifty tool tray in the top by notching the three top pieces with a jigsaw. Clamp every 8 in. or so before driving in the 3-in.deck screws. Predrill the screw holes near the ends to prevent splitting. When you’re screwing on the 7-in. long 2x4s to create the leg slots, use a scrap piece of 2×4 as a spacer.
This Vermont Farmhouse by Real Good Toys is as pretty as the real thing. And if the seven-room home isn't big enough for the serial renovator in your kid, the site also sells additions that add two rooms to either end of the house. Just like the homes old-house lovers hope to own, this farmhouse comes with real wood shingles, wood floors, interior crown molding and a spacious porch.
After I left the magazine for a new job, I did all of my woodworking in my small two-car garage, but it was a struggle. Power, lighting, and temperature control were limited. And because I shared space with our cars I was always moving machines around, often while in the middle of a project. On top of that, my tool and machine collection had long since eclipsed the space. For all these reasons, fixing up the garage wasn’t an option. My finished basement is a family room, so it was out, too. An addition to the home or a stand-alone building would have been too expensive. I had to find a better path to a shop.