I can't see the point of plastering garage walls, I didn't even paint mine, but we did specify 'fair-faced' blocks. If your blockwork is a bit pants I would just paint them with an exterior emulsion.
I went for a plastered ceiling though, and fitted plenty of LED battens
Not sure why you don't like interlocking tiles, I love mine. Easy to look after, comfy to kneel on.
As for a door, I went for insulated roller shutters with high-security channels. They cannot be jacked or levered open, and don't occupy ceiling space when open.
