Tile layout and other questions

Hi Guys,
Being a relative novice to the art of tiling, I am here hoping to glean a few tips and techniques in the art of shower recess and bathroom tiling.
The builders are here (sometimes) to repair flood damage under insurance and are doing a few properties at once.Hence they are here one day and then gone for a week. I am taking advantage of this and upgrading the bathroom which was fairly tacky.

Just to make things difficult there is a small window 500H x 350W in the shower recess above head level.

Other shower recesses I have looked at seem to have a layout where the full tile is on vertical center line of the wall and have equal split tiles at the wall edges.

That seems to be standard and would appear logical in giving the appearance some balance.

What I am not so sure about is where about to take the datum line from.
I am thinking in using the lower widow ledge reveal as the datum. I have had a pro in to wetseal the shower base and he will return to lay the floor bedding for the non slip tiles. I hope to complete the wall tiles to co-ordinate with his expected return to we can have a shower instead of sponge bathing from a bucket.

The old bathroom was lined in slash pine tongue and groove and had been subject to white ant attack.The reveals were pine as well so they were ripped out.

Question? Can i tile over the hardwood frame that the window(aluminium) is fitted to? The window is well above shower head level.

The frame is not level so I am taking levels from the high corner with a allowance for some adhesive under the tile.
I have calculated 4mm adhesive under the high side and 8mm on the other low end.

Question Is this sufficient amount of.

Question .Is centralising the tile lay out on the vertical centerline the norm. The down side of that is that the tile joints fall over the shower taps.

Advice on these questions and any other information you would care to put forward would be of value to me .
Thanks


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