Welcome to gardening in the major leagues. While I'm still a rookie, I would opt for getting things in the ground as soon as you can be assured that you can work around them without too much trouble. Of course it would be nice to have everything neat and tidy and dead first, but if you go that route you may never get anything planted.
I like to get things in as soon as I can, and get the meter running on the slower stuff. But it doesn't pay if you have to work around them while doing the more detailed work.
Stabilizing a slope would be too hard to answer without seeing the specifics. But generally you can move rock (if you have enough) or use some ohia logs with re-bar for stakes, or whatever you have. As you have seen, you can do magic with rock work, but it is slow, hard, heavy work, and be sure to watch out for your fingers.
For the stuff you are cutting and want to die, most of us use Crossbow - an herbicide you can paint on the fresh stumps and will kill most everything. Full strength or half and half with diesel works. It's not cheap, so I go the half and half. You may have to treat tenacious stuff like guava twice.
Other than that, it's hard to offer specifics without knowing the situation. Or sometimes more importantly, the situation underground.
I'll have some more pics soon of the almost finished project. As you said a small job has extended and grown to almost a month now (six half days a week), and that even includes a excavator I brought in for 13 hours (that sent me to the emergency room one afternoon for stitches in the head). Almost $1000 of cinder for the pathways, and something you don't worry about - irrigation valves, controllers, and about a thousand feet of tubing. But the excavator could get to about twenty places that I needed holes, so that will save a lot of digging time. It can make a hole in about 30 seconds that takes me 30-40 mins with an o'o bar. You may consider hiring a small excavator. Jerry had a guy come in with a small one he was really happy with. You could get more done in a day than you could in a month otherwise.