Here's a good starting point for a gelatin "glop".

8% gelatin, 5% yellow food coloring (I've been using McCormick's), 1% sorbitol (you can just use sugar).

A Mayer rod (meyer rod, wire wound rod, metering rod, etc.) is great but by no means necessary. Take your film base, tape it around the edges with masking tape to a leveled piece of glass, pour on about 0.5mL/inē and spread around with your finger or, what I've found to work really well, a comb.

I'm sure you can find some potassium or ammonium dichromate somewhere, but if you can't you could look into using diazo sensitizers (but that's a whole 'nother project in itself!)

As for "what dyes imbibe", well that's a tough answer to give succinctly, and I'm not even really sure if I know the answer. There are a couple (1 potato, 2 potato) dye-imbibition threads that I've created in the past. There's a huge list of dyes (above) and then there are the ones mentioned in this most recent BJoP article.

But it's true that any dye related to dye-imbibition (dye transfer) is going to be cyan, magenta or yellow, and suited for relief matrices and not planographic matrices (though we can't be sure until we test).

Textile dyes are probably the best place to look from a hobbyist perspective. Check these out...