I like System Three, but epoxy is pretty much epoxy, so if you can find one that mixes 1:1 or 1:2, its easier than some of the new formulations that are 1:5 when mixing small batches.* You don't need much for this project and you can probably get it at West Marine.* Quite honestly, given the small amount you need and the fact that you aren't doing anything structural, I wouldn't shy away from tubes available at the hardware store.* Just don't get the 5 minute stuff, as you need 20 minutes or so to mix it, apply it, etc.* If you have more projects to do, buy the smallest amount available from West Marine and keep it on hand.*
To get the sanding dust, from your photo it looks like the door could be refinished, if you have an orbital sander with a bag, you'll make the dust you need easily enough.* Use 180 grit.* If you don't have an orbital sander, and you have other maintenance projects like this, buy one.* I have a few, and like the deWalt DW421 the best.