We're about to start tiling a kitchen floor but are getting a bit confused! We've got 12mm ply to fix down over the existing chipboard floor, but are unsure where (or if) we need to prime first.
The adhesive we've bought is Mapei Buildfix.
The tiles are 330x330 ceramic.
The primer we've bought is Mapei Primer G.

OK, here goes with the questions....

Is it right to leave 5mm expansion gap at edges of ply, and 2-3mm between?
Are we OK screwing down at 300mm intervals or is more frequently needed?
Some threads say there's no need to prime with this adhesive, but others are saying it's needed?
If we do need to prime, do we just do back and sides? and what's the purpose?
Some are saying this primer isn't suitable for ply, others are saying they often use it?

Many thanks in advance for any help offered

The only information I can provide is the way I would prepare it, and that would depend on the stability of the floor!
I'd overboard the floor with 6mm Hardi tilebacker boards to a deflection free floor.
This type of product has changed the way tiles are fixed and eliminated the movement we used to find in plywood.
Hope this helps.

as Timeless John for me

yep hardi backer for me as well

if you are going to prime the ply S.B.R primer. dont forget flexi grout as well!!