I laminate all my backs and sides, it's the preferred thing for the Selmer style guitars I make. I laminate both 15' radius spherical backs and vaulted backs ala an archtop. The degree of recurve in edges is what mostly drives the amount of darting that needs to be done.
I use three or five layers depending on the thickness I want. I use poplar for the middle layers in either .5mm or 1.0mm thickness. For the inner layer I use .5mm mahogany. I buy the poplar and mahogany veneers in widths that allow full width and length without a joint. If there is to be only one middle layer, I offset the grain 90 degrees . If two, I offset them 45 and -45. If three, I go 90 degress, 0 degrees, 90. Balancing the grain directions is important otherwise, the part will warp. An example of an unbalanced laminate would be three layers parallel at 0 degrees and one at 90, this would be likely to warp.
If the recurve is severe enough to cause puckers in spite of the darts (it happens), laminate the inner layers first, all but the outside layer, then fair it down before adding the last layer in a second laminating operation. One layer of veneer will go do with some coaxing as the vacuum is drawn even with a lot of recurve. If the outer layer insists on puckering, it will usually crack the veneer, so I test-vacuum the last layer down dry and see how it behaves. If it does pucker, it will usually stand the veneer up a bit and crack. From then on, it will always happen in the same spot, so pull the veneers out and open the crack up a bit with a sharp blade to give it some relief. In dark woods, you will seldom see it. In maple, it will be pretty obvious no matter what you do. I have rejected more than one maple laminated back. Or go for a dark edge tobacco burst in the finish.
All that said, I have started using molds with more modest recurve and height. At first, I thought this would be a sacrilege and maybe it is, but no one seems to notice. These laminate up in one shot, never a wrinkle, easy peasy.
I like epoxy, WEST 105 with fast 205 hardener. Even though it is fast hardener, there is plenty of working time. Sets up hard enough to remove from the vacuum in four hours (at 70 deg F) and fully cured in eight. I had no end to trouble with water base glues: short working time, messy, hydration, warping, finish spitting later as the veneer dried out. Epoxy is much better. Apply with a foam roller designed for epoxy application. WEST makes them but so does Woolsey (cheaper). I use 25 grams of mixed resin for each interface, so if I have a three ply laminate, it has two interfaces, 50 grams. I apply epoxy to both surfaces of the interface. With the right amount, you will get very little squeeze out, a super bond and a minimum of added weight.
The key to getting epoxy to work well is the measure it accurately in small batches. I mix epoxy using a cheap ($12 Amazon) digital scale that measures to the hundredth of a gram and I try to get to get it right to the hundredth. One drop is about 0.03 grams, so it can be done. I routinely mix 5 gram batches for small jobs.
Regarding the center line joining where necessary, I glue the edges of veneer together with Titebond. Rough cut the edges with a straight edge and veneer saw or razor, then joint edge with a sandpaper beam. Use tape to hold the edges together until the glue kicks and then pull the tape. This will hold up to the rigors of vacuum molding. If the tape ends up on the outside, leaving it on is no problem.
My molds are male. I glue a piece of 3/4" 6 pound density urethane foam down on a 3/4" piece of MDF and carve the foam down to the MDF. The MDF represents the edges. Coat the foam with a couple coats of epoxy and wax it. I use vacuum bag and coarse bleeder cloth, no top side mold.
Epoxy will squeeze out through the pore of the inner and outer layers. If you pull the part after about four hours, the green epoxy will scrap off relatively easily. I then clamp the part back on the mold to finish curing. Epoxy will darken the wood, but if you use epoxy to grain fill, it will blend in perfectly. As the veneer is thin, you don't want to do a lot of sanding to level. Even with a good vacuum, woods with curl or figure like birdseye will not flatten completely and sand it fully smooth might break through, so epoxy grain fill here is your friend and will help level the surface without break through. I use WEST 105 resin and 207 clear hardener. Fully cures in 24 hours, very little amine blush.
Final thought: you will have some failures, I certainly did. Wrinkles, cracks, splits in the top veneer, etc. Try to finesse them but if not acceptable, ditch it and try again. Sometimes you can save a bad one and add another layer sometime when you want a thicker laminate. After the first 6-8 backs, you'll work it out and gets good ones (most) every time.
) I always assumed making a laminate plate would be trivially easy and not at all real woodworking. So then I decided to bang one out. Suddenly I realize that it is not so trivial 
