This is a hefty job really thinking about it. I'd make sure you price accordingly. Your standard rate needs to be almost double in my opinion. And ensure you let the customer know the materials are more expensive too, I guess the customer would have already been advised this by the tile shop though.
Watch out for trying to get the floor tiles line up with the wall tiles. It's bloody hard work, so I'd ask if you can go diamond on the floor and square on the walls or something. Or spend a fair bit of time on the set out and set both the walls and floors out at the same time if you are requested to get the wall tile joints line with the floor ones.
Wediboard - Bloody brilliant stuff and will carry more weight than plasterboard I believe as it is cement based and has extra grunt due to the structure of it.
If the floor has been overlay-ed with plywood, you should be ok with flatness I think, and the walls similar really. Just use a large format trowel if that's the case and bed those tricky ones where a screw or something is not helping you.
If the wedi is to create a wet room type affair and is meant to be sealed. Make sure the wedi jointing tape and wedi screw are used as per the wedi guarantee.
I'd still perhaps tank the last 12 inches near a shower tray though etc. Just to get the wall part of the tray and water running down the wedi then will fall into the tray.
That's all i can think of off the top of my head
