Please don't forget you must have really good drains for this extra water load. Have you considered a tankless water heater? Or at least a separate water heater for the master so that the rest if the household still has a hot water supply and pressure balance. That's something to consider also. I've often wondered, I must admit, how all of this is supposed to work with energy saving measures in place.

No. If you really want a shower fixture, make sure there's a drain and a sloping floor (so no glass door or shower pan) and just hang a fixture on a reasonable sized piece of wall. And consider the costs, how long you planned on living there, will you use it for more than spraying plants or washing the dog, etc.

What's the height of your bathroom and which geyser type ( horizontal or vertical ) you are using at present, all depends on these two things. If you've not bought the geyser then you can opt for horizontal one for the convenience of installing a false ceiling and then on one wall install the geyser. OR You can have a FLAP customize beneath the geyser for the maintenance and have the false ceiling too. For any query, you can revert back.

If the shower area is sufficiently big, I would prefer to opt for glass partition as that ensures that outside dry area does not get wet, which may happen in case of shower curtain. Having said that, I would opt for shower curtain if the shower area is small to avoid accidentally banging my elbow against the glass partition while taking shower and getting hurt.