Congrats on the new tank.
I would start off with 1.5 lbs per gal
of live rock and see what it looks like. Anything over 1 pound will provide your biological filtration, and if you can push it close to 2 lbs, even better. Remember that there is different types of LR
with varying densities and this will ultimately be the deciding factor about how much LR
you can get away with. You want to keep a good amount of water in a nano and not be shortchanged because of too much rock.
Also, try to get smaller pieces of LR
which will give you more aquascaping options.
in my opinion is a waste of extra money. Just buy some sugar grain aragonite and seed it with a cup of live sand from an established tank.
Your lights give you 3 watts per gallon which isn't terrible nor is it enough to keep high light demanding corals. You'll get away with lots of softies and such, and you may be able to try some LPS
. I'd stick with what you got and only upgrade when you're sure you need to.