Most places sell 1 1/2" junction boxes.

Right. Stupid me.

If you don't mind.

After we lay the Hat Channels, what is the best way to cut openings through the sides to run the electrical?

When dropping a 12' x 8' foot cement bases ceiling in a condo, what spacing do you recommend for 12 foot, or 8 foot, runs?

We're using drywall for the new ceiling.

Would the shorter 8' run be easier to install, and/or stronger?

Is 25 guage okay, or better with 25?

The building would like us to glue the Hat Channels to the ceiling using as few "pins" as possible.

Does the glue work well when the cement is painted?

Appreciate the help.
Thanks.

Ops. 20 or 25 guage.

If you have 1/2" drywall + the 1 1/2" hat, you have 2" for the box depth. The box itself can be many different styles, it all depends on how many/what gauge of cables are in the box to keep within the allowable box fill requirements. It can be as skinny as a pancake box. Note that junction boxes have to remain accessible. It sounds like there should be an electrician involved.

Do not bore a hole through a hat channel for cabling, run cabling parallel towards a wall or provide consistent gaps in framing layout. Or go to a resilient channel. If you rely on glue for attachment make sure to wear hardhats all the time.