I’m surprised by people saying that more than 50% or 80% infil doesn’t help.
In my experience, 100% infill is important. It greatly increases compressive strength horizontal to layers. And it will greatly increase layer adhesion.
BUT this is only the case for some filaments. PLA will not benefit strongly from 100% infil (although I still would do it to be safe). Other filaments such as ABS are very difficult to print large pieces in 100%. Others like PETG, PET+, and Edge (based off of PETG, which is polyester) will become stronger. Edge will become a solid piece of plastic at 100% infil, will be impossible to delaminate, and will effectively be as strong as an injection molded part.
I highly recommend edge by e3d. It’s the only thing I use for ESK8 and have full faith in it for wheel pulleys and entire enclosures. Had several nasty crashes and never broken a printed part.
Here’s a picture of a break through layers of 100% infil. It should make sense why a solid piece will be stronger with this material.
Now onto some more detail…
From my experience, the more wall surface area, the harder the print will be to make. Printers will try and make nice outer faces and typically run slower on these exposed layers. You can cut down on weight by decreasing infil, or by creating a lattice inside.
Based off of your description, I would recommend a honeycomb shaped pocketing of the part. I’d say leave 0.125 - 0.25 inch wall thickness between the hexagons, which leave the part ~50% air by volume where pocketed. On the outer edge of the part, I think a solid 0.25 inch thickness is good.
Also, I’m interested in this print. I’d do it for you, I’m actually on a flight home right now and will have access to my printer again soon. Let me know any way I can help, feel free to bring this to PM if you’d like. My size limits are 8x10x12 inches, but parts can be split up.