HI First post on this forum. Experienced DIYer but first wetroom.

5mx2m 1st floor, wooden joist, 25mm ext. ply. 20mm Marmox with showerlay. elec UFH.
Plan is to lay the showerlay on a bed of c2fs1 tile adhesive (larson) to stand proud of the rest of the floor, so I can lay the UFH and SLC (4mm) to finish level then tape and seal joins with mira safecoat/multicoat, to give a flush surface to tile (600x600 full body matt porcelain).
Walls back to brick - dot and dab 20mm marmox and fix with marmox dowels.

Q1 Info from marmox is not consistant, should I use tile adhesive and screw/washer the rest of the floor or would one or the other be sufficient.
Q2 Presume I should continue the latex tanking as far up / out over the slc as tub will go.
Q3 I have a BAL tipped trowel ( leaves solid layer with little ridges) could I use this for the floor and wall or would I better off buying a 20mm solid bed trowel for the floor and standard square slot trowel for the walls. Never used tiles this big before (walls and floor).
Q4 is it ok to transition from marmox to plaster board half way along the long wall, or just pay the extra and marmox the whole room (as its already stripped back).
Q5 anyone got tips on getting these small marmox boards as flat as poss using dot and dab and marmox sealer between sheets.

Thanks

Use the washers with screws on the boards.. Approx 9 fixings per board i find ok..

Use a 10mm solid bed trowel U notch.. 10mm deep/20mm across type.

I would pay the extra for marmox and leave PB out of the equation.

Use a long strait edge to tamp the boards flat on the walls.. leave to set before inserting dowels..

The rest seems fine.

As above for installation, but you can get larger sheets of Marmox in 600x2400....

Yes I looked for larger sheets but couldn't find anyone that stocked 20mm in large size. so got a bulk load of all same size and thickness.

Extra Q should I tape and mira multicoat ALL joins on the shower walls or will the marmox sealant (between boards) and tile adhesive be enough??!

I always tape joints in wet area's......

Finally got round to this project and but want to make sure before tanking..

I have marmox then ufh embedded in SLC (mira x-plan) do I need to prime the SLC before tanking with Mira tanking?! multicoat.

you need to check the tanking is suitable for use with UFH..

Ask far as I can see from data sheets mira multicoat is ok with heated substrates, but it states "Absorptive substrates should be primed with mira 4180 sealer", just not sure if x-plan SLC counts as an absorptive substrate, presume it does, just don't have primer to hand.

slc would be absorptive so i would prime it just to make sure