Bowed 2x4s in attic: are these really doing what I think they are

The attic needs to be able to breath to reduce the heat buildup during the summer and prevent condensation and ice dams in the winter. So don't do anything that would block the air flow from the soffit to ridge vent, and don't place anything in direct contact with the roof. The result is that the rafters shouldn't have any storage items installed between them.

The next concern is floor load. If the attic wasn't originally installed with a floor, it's very possible it's not designed to support the load from a lot of storage. If you ignore this concern, I would make an effort to find any load bearing walls below and build the shelves directly on top of those.

For lighting, my preference is for a single bulb to light the attic space and then use a headlamp to look into the various crevices. But then I'm not up there often enough to make a more permanent solution worthwhile.

One last note, make sure any items you do store up there are capable of enduring the temperature and humidity swings, don't have batteries in them, etc.

Yes. Very possible. It has to be engineered though. We have plans to do just this. The drawings and engineering cost around $1000. I wouldn't try it unless an engineer has looked at it, drawn a plan and signed off on it.

For us we are going over a 3 car garage and the roof pitch is 12-12. So a lot of space there. The plan is to remove the drywall ceiling in the garage and install 24" engineered joists (2x4's). We lose a little head room in the garage and the space above, but not much.

Then once the floor system is in place it's much easier to move around. 2x6 rafters installed with collar ties at about 8.5 feet, and plywood gussets with engineered nailing patterns at the peaks. Then cut away the trusses. Doing it for about $80 a foot, and it will add about 500 square feet.