Tiling onto plasterboard and Plywood

[tcm]

In the hopefully not too distant future I'm going to have some tiling to do in a small cloakroom.
I'm not doing the whole room just around the toilet, sink and some pipework but am unsure about how to prep the surfaces.
Will it matter if I have already painted the plasterboard with a few coats of water based paint or is it better if I steer clear of the area I'm going to tile when I paint?
Or should I prep the plasterboard another way?
The other area to be tiled is basic plywood. I know it's not an ideal surface but it's what I already had left.
Should I be applying a primer to one or both sides of the ply before tiling or something else or just leaving it?
Will I need to look out for a particular adhesive for either surface or will any basic premix do?
Thanks for the help.

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[tcm]

Can anyone offer any advice on the above?
If the plywood needs priming before tiling I'm hoping to get it done when there is a break in the rain later this week.

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