I want to soundproof my basement as much as possible. I will be
moving a band in to rehearse and I want it to stay quiet as possible
upstairs, this is my #1 priority.

My plan is to stuff the cavities between the joists with fiberglass
batting, I assume a higher R rating will be better? After that, I'd
like to run rubber strips or something along the bottoms of the
joists, then screw 2 layers of drywall to it with a layer of 'green
glue' in between. I know it won't be silent upstairs, but this would
be an acceptable level of soundproofing for my purposes.

My concern is that the joists are not standard 2x12's or whatever,
they're I-joists - 2x3's on the top/botton, and what looks like a 10"
or so strip of Norboard in between. I was told a year ago not to hang
weight from the bottom of I-joists, because while they're strong when
you push on them, they are NOT strong when you PULL on them.

So, by my guesstimates and calculations - lets say a sheet of drywall
is 40 lbs. 2 sheets thick is 80 lbs every 4x8 section, which is 2.5
lbs per sq. ft. That's a total of 750 lbs if drywall on the whole
thing. All that batting is going to add weight too, not sure how
much, maybe 100 lbs?

Will this be safe? Any alternatives?

tia,