wood rots when in contact with earth. dry rot will happen when in contact with concrete. so the way to prevent rot is to use a concrete pier until floor is above the earth, and then use a resilient sill plate such as preservative treated lumber for pieces in contact with concrete. alternative is to use a raised post base bracket such as made by Simpson.

yeah, i built one similar to that so i could wheel it out whenever i needed power tool access. the 2000W inverter is able to start all the tools i own, and has a built-in charger function. https://www.reddit.com/r/SolarDIY/comments/10r7up0/diy_battery_backup_cart/

i used a wallpaper steamer for this (along with all the PPE). it worked fine, a bit of water was absorbed by floor boards but no damage after letting it dry out.

it is possible if you hire a professional to review the changes to the foor framing and design a new load path, but that is a lot of work just to mount a projector. i'd find a new way to do it.

sounds like you first need something for bulk. make a cement paste using epoxy and bits of another solid material, such as old bricks or stone.

for the other issue where you can't get a nut on the backside, there are commercial products which use a plastic screen to form a plug on the backside of the wall material, which you can also improvise. (example: https://www.strongtie.com/screentubes_adhesiveanchoringaccessories/optimesh_screentube/p/opti-mesh-adhesive-anchoring-screen-tubes)