I can answer some of your questions as i have a Defender II see here, and i am sure Mike will be along and correct them and add to them later.
https://www.candlepowerforums.com/threads/165790
You will only get your 2 stages of output from the Defender II or i think mike is about to release a weapons version which has a high/strobe output
If you are only running the 1 x 18650 then you are better off to buy the 3.7-6V LA (which is the LA that comes with the Defender II), as i understand it the 3.7-13V LA is not regulated with a single 18650.
Mike has already quoted runtimes for the LA, although he hasn't for the Defender II, i believe he isn't stocking it, runtime on high is the same at 110 minutes regulated with 30 mintues unregulated and low is quoted at 20 lumens for 50 hours. Never tried this myself.