1) If you've labeled words, the label will appear the "view all" select box. Opening it and selecting your label will load all of the words with that label onto the screen for editing. At that point, you can click on "Flashcards" or "Review" without selecting individual words to review the whole category.

2 + 2a) Yeah, it works (we've tested and Mike has too I think). But only exporting. The IPR licensing of the ABC dictionary means you can't actually export definitions from Pleco. Pleco has an Adso dictionary addon that comes from our site, so a decent amount of stuff can be optionally installed there automatically without the need for manually exporting wordlists.

3) If there are words checked but no label specified, you will be tested on the checked words. If you've selected a label, that will override the individual word selection. This looks like a bug.