Welcome. Many plates come predrilled for standard mounting holes, mostly based on two standard placements. You will be removing the plastic base plate already on the router, so save the screws and fit them to the plate. Not certain that Skill uses standard screw placement, but you can contact them and ask. Then you can buy a predrilled plate.
Whatever plate you get, get one with a twist lock (Bayonet) insert. Most do, but a few still use the three tiny screws to hold the insert in place. The technical name for these is "Where the hell did that screw go?" The twist lock eliminates that problem.
Or you can buy a blank plate, use the plastic base to mark the hole positions with a punch, then drill them out. If the screws (or miniature nuts) have a cap, drill the hole slightly larger (1/32 nd) then drill a second hole on top just a little larger than the bolt head. See illustration. This allows for a little error.
Whichever way you go, keep the base plate you removed because you will need to put it back on if you have to use it hand held. I seldom use a full sized router for simple tasks anymore, and use a small trim router instead. These are very inexpensive.
I suggest you NOT bold or screw down this plate so you can lift it out to change speed and bits. Much easier to do that way.
Making your own table can be very simple. Do find and use Baltic Birch ply if you can find it. Make sure it is flat, some precut stuff is stored improperly and is not flat. I suggest you do two layers, top 1/2 inch, bottom 3/4. Cut the opening in the top just slightly larger than the plate (too tight and it will be hard to get out. lay it out on the bottom piece so the two same-size pieces are aligned, then draw a pencil line onto the bottom layer. Separate the pieces, mark a second line half an inch inside the first, then cut that out. Lay tape on the top when you make the cut to limit tear out. Drill holes in the corners with a Forstner bit if you have it, about the size of the curve on the plate. Sand and smooth the opening on the top after cutting with a jig saw.
Glue the two pieces together.
You'll need to add leveling screws of some sort up through the bottom layer on the rabbit you have formed. They make the plate level with the top, or use some Kreg levelers as shown.
Making a fence can be simple or complex. The key is that the fence face MUST be straight. And you need to cut an opening in the center for the bit. Make an L shaped fence by gluing two pieces together with square blocks to brace the fence at a 90 degree angle. That will give you a base you can clamp to the table. With that setup, you can buy a 2.5 inch hose attachment to suck the sawdust away from your work.
You will always need something to measure a 90 degree angle, and a really good plastic triangle will do for many uses. On the bottom front of the fence, cut or sand away a 45 degree by about 1/8th piece so sawdust has someplace to go. Sweep away sawdust atop the table before every pass you make. Sawdust under your workpiece will cause small differences between pieces which show up if you butt two pieces together.
Once done, wax the surface of the table and buff the heck out of it.
All of this is far simpler than it sounds. And your cost will likely be $70 or so, depending on the plate you choose, the leveling screws and a 2.5 inch dust port. You could do without the plate, but it will not be as convenient.
Making your own router table is almost a right of passage and it can provide some basic lessons in working with wood.