I use standard narrow angle LEDs, because I didn't find any wide ones at the time, I built it into an old scanner ripped off a multifunction printer (I also used the power supply ripped out of the printer as it happens).
Because of the very limited distance between glass and the bottom of the scanner and that they were 20 degree angle LEDs I had to really pack the LED's in very close to each other so as to not create dark spots (I worked it out as to how close they needed to be first). 100 LEDs didn't go far, a 5x6 is about the best I can manage with it. More than that at the moment and I wait for a nice sunny day :-)
I've got another hundred or two to put in sometime but those wide angle ones look quite nice, would be able to spread them out much further, almost enough to make me want to start again.
I've also seen (I think on hackaday, or maybe dangerousprototypes) somebody use a UV version of that self adhesive LED strip you can buy, easier than soldering a couple hundred LED's, but probably expensive.
My box is only single sided, to do repeat exposures for double side or soldermask I use registration markers on the artwork in one corner (which appears in the same place on all the generated artwork, etch top/bottom, mask top/bottom..), I tape the artwork down to the glass, and then I have a corner cut from a transparent plastic set-square from the dollar shop that I tape down exactly over the registration marks, that way I can just butt the appropriate corner of the PCB into the "squared corner" and tape a presser on the opposite corner to hold it hard against it.
I find this to be the best way to get a "mechanical" alignment, without actually pre-drilling alignment holes and some sort of pinning setup.