2-part mold for modular game board sections with holes

I want to make copies of a board game I invented. I already have laser cut masters for each of the 10 board sections. The sections can be rearranged in a variety of ways, to produce different overall shapes.  >>>here<<< is an image of some possible ways to put the sections together. The sections range in size from one game "cell" to 18 cells. There are 91 cells total to build the board with.

In order for this to work the way I want, both the bottom surface and the top surface must be smooth, flat, and parallel to each other. All the sections must also be the same thickness, so that as long as the table you play on is smooth and flat, The board surface will also be smooth and flat regardless of hopw the sections are arranged. The holes need to be positioned precisely in order to hold the special game tiles in place. For now, though, I'm not asking about how to make the tiles, just the board sections.

Each master section is in two parts, which I have not yet glued together. The main part of each section has holes cut entirely through it. My initial idea was to have a backplate on each section, so the holes would not go entirely through the final product. But I'm not sure I will get the accuracy I need if I try that. The Alumilite instructions for a 2-part mold tell me I should first make a mold that entirely surrounds the master, and then cut the mold into two parts, along some plane such that this cut line will not be noticeable. But consider for example the 18-cell section I need to make a mold for. The master, without a backplate, measures about 12" by 5" by 1/8". Take a look at all the fiddly little nooks and crannies that each section has. I would have to makemy cut horizontal and between the top and bottom surfaces of the board. How could I make this cut? The blade would have to be very sharp and at least 5" long. I don't want to "saw" at the mold while I make this cut, because I don't want to grind away any portion. Maybe some kind of thin wire, made hot by passing electricity through it, would produce the clean cut I need. I have seen this method used to cut Styrofoam shapes for radio controlled model gliders. But that would be a huge hassle to set up. And the hot wire might melt away too much of the mold, so that different sections would not be the same thickness.

Then it occured to me, what if the lower surface of the top part of this 2 part mold were completely flat and smooth? I wouldn't have to make any cut at all. Here's the method I propose to use. I welcome any comments, advice, suggestions, or constructive criticism.

First, instead of gluing on a back (or bottom) plate which follows the same convoluted perimeter as the main part, I glue a front (or top) plate onto each master section, with a hole drilled at each of the board holes. This top plate would be rectangular and would extend to the boundaries of the box I pour the mold into. (The masters are all mde of clear plastic BTW.) I have to devise a method to hold the top surface of this plate in place, parallel to the bottom surface of the mold box, so that the master will not sink to the bottom while the mold is hardening. Because of all the nooks and crannies, this lower mold should probably be flexible. All the vertical surfaces are normal to the top and bottom, so I don't have to deal with any undercutting. I pour the mold into the box and then push the master into it untill I see mold material coming out of all the drill holes, with no air bubbles. Then I lock the master into place, suspended above the bottom surface of the box.

To make the top part of the mold, I want a mold material which is as stiff as possible, to minimize any "sag" into areas where it will not be supported during the casting process. I want this upper mold thick enough to avoid sag for most of the board, but around the perimeter, where the nooks & crannies are, I want the mold to be thinner, so that it will be easier to make pinholes where I want them, and also easier to see when the resin comos out of every pinhole during casting. In order to do that, I use the same master piece with its attached top plate, but I flip this piece over. The top surface will have strips of wood glued to it, to make the top surface of the top mold thinner in the places I want. This is why I want all my top plates to be rectangular in shape, so I can flip them over and produce a top mold which will match up with the bottom mold.

Before I start casting, of coulrse I will have to smooth down all the bumps where the mold went through the air holes.

I'm concerned about surface tension of the casting resin during casting. I want the resin to come out of every pinhole in the nooks and crannies. I'm thinking ot using Alumilite White with a few drops of blue dye mixed in. Is there some other resin that might work better? Would it help if I vibrate the table during pouring?

Thanks for your input!