I don't know how I missed this thread before.
HUGE congrats on your home at your age. I was fortunate to do the same.
A couple comments on "trussing" your ceiling joists. When I did my overhead space on my last home (older like yours) I added joists like you did. Then to tie them to the rafters, I SLIGHTLY (< 1") jacked them up from below with my floor jack and a long 2x4 and used plumber's tape (you know that that is? Sheet metal tape with holes in it) and self drilling caphead screws. I attached the tape to the rafter with a couple screws, wound it under the joist and back up to the rafter again. I did this at 1/3's on each new joist I had added. The "lift" only served to straighten the plumbers tape and mildly preload the joist so its weight carrying capacity was increased. I only stored very light weight things up there and out toward the walls around the perimeter. Things like Christmas/seasonal decorations (what am I saying,...you're not married!), ice chests and camping equipment. Saved a TON of space in the garage.
What are your plans for finishing the interior? Paint? Color scheme? Your floor probably has no vapor barrier so epoxy may be out of the question but vinyl or ceramic tile like Jack Olsen's might work really well if you can swing it financially.
Best of luck, you're doing GREAT.
