Yes, you should. I don't know about kangaroo paws (aren't they a CA native?) but I'm quite familiar with cutting into / planting in the delightful and rock-ridden SouCal clay pan.

I'd contact a local garden club through their website to see if they have tips (normally I'd suggest you join a C&S club or at least attend a meeting, but they're not happening now).

Short answer - no sand. NONE, as it's not useful in this situation. The best would be small gravel/decomposed granite and pumice, along with some sieved top soil to use as soil amendments - what you want is some of that clay in the mix, but mostly the other things, particularly the DG and/or pumice. Amend the yard as you need to - the planting locations need it, not necessarily all of it.

Oh, and get a digging bar if you're going to do a lot of this. It's invaluable in punching planting places into the ground.

I think your chalk plants are Senecios.

I like them a lot, but wasn't successful growing them in pot, and spending 6mo indoors in my location...They are native to SW Australia IIRC. They prefer slightly acidic, well draining soil, and lots of sun. Most succulents do.

"They are native to SW Australia IIRC. "

Yep. Not too many kangaroos in SoCal........ :-))