The piping has to be the exact same length for each shower head from the tee where the cold and hot water feeds from the top of the diverter faucet.
Depends what the Shower pressure is, also how much dirt is in the water and the size of the shower holes
If it is a gravity fed shower raise the tank or use a shower pump in the loft. If its off a combi boiler you cant without butting a bigger out put boiler in. If its a electric shower put a higher kw shower in (may need lager wire installing). or simple descale you're shower head.
If you have a new pressurised water system there is a possibility that the added water pressure could cause a leak.
If it is indoors and not a recessed shower, you may have a leaking shower pan.
Installing a steam shower in the basement is not a good idea. The steam shower should be installed in the nbathroom of your home.
As long as you are using the same size supply line there shouldn't be any difference.
A leaking shower valve by installing a new cartridge.
pressure and humidity
On some of them, you may need silicone to seal the lowest seam. Depends on the design of shower base.
Yes it is etiquette to have a bridal shower for a second wedding.
By installing more then 3 flow restrictors
This does vary slightly according to the shower, but for a shower without a pump, using a gravity feed, a water pressure of at least 0.1 bar is recommended. If your water pressure is low you will need to install a pumped shower.