Basement ceiling.

Does your local ordinances specifically state you must use 5/8" ? Few residences require it, more only in multi family (apartments) or commercial buildings.

Mind you if you can do it, 5/8" always give a nicer finish, and stops more noise.

While I personally like drywall instead of ceiling panels, if you have electrical boxes scattered around it you do have to leave them accessible so the dropped ceiling may be your best bet.

Once again fire regulations are different for homes so the plastic strips may be fine. If in doubt, phone your fire department.

AMUN

Makes you wonder about that. I'd use 1/2" because it is easier to handle and is still much better that having nothing. Thinner is just too flimsy though, IMO.

Some plastics can take high heat. While it is not banned from use, I doubt it makes a barrier according to fire codes though.

Yes, it is against code to put permanent coverings over them. Dropped ceilings make a lot of sense because in the future you may want to add wiring, plumbing, who knows what.

I don't understand why a fire separation is necessary. Are you parking cars in the basement? Fire separations between occupancy ratings are required, like in the case of a garage and living quarters. If your local jurisdiction requires a firewall between single family residential stories, perhaps you could let us know what country you are in? In the USA, such a separation is not required, unless each story is a separate dwelling unit, like an apartment.

That said, there is 5/8" sheetrock that is not type X. It may be that

There may be drop ceilings that are fire rated, but not with plastic components.

Yes. If you use gyp board, you will need to move the junction boxes into the face of the board and install the appropriate cover plates.

I hired a contractor to install a drop ceiling in our basement. It is suspended a few inches below the floor joyce in order to accommodate drop in fluorescent light fixtures. The ceiling consists of metal frame with drop in tiles.