Have not myself tried RWS as a sauce thickener. Have used xanthan gum all 9 years I've been low-carbing to thicken. Glucomannan gets way too thick way too fast for me to like using it.

Regular shortening isn't as healthy as palm shortening. But regular will sure work.

Re spreading the focaccia batter, no, that's the part I hate, too. Low-carb batters can be such a PIA that way, having "special handling" because of the texture (or lack thereof). I use a spatula to spread the batter out from the middle at first. Then I switch to a fork to spread it up along the edges to my desired size. I find thinner is better, as it DOES rise during baking (whereas many LC pizza crusts do not rise much at all. I don't go all the way out the full 16" pan size, but I get mine to about 14" most of the time when I'm patient with the process. I just hold the parchment down steady with a finger on my free hand. I'm old school in the kitchen and use the "tools" that are the handiest or that take less interruption/time. LOL