Both
48" for a shower and 15" above the tub for a tub.
yes
Most shower curtains cover tubs that are 14 inches wide. The shower curtain should be where the tub "ends" and should be hung 7-8 inches from the ceiling.
The difference between a shower and a tub is the shower tends to enclosed with water that comes out of a shower head above while a tub has a faucet that pours into a large basin.
Bath tubs don't necessarily contain a shower, and a shower may not have a bath tub. Shower tubs are a combination bathtub and shower; the shower head is usually mounted above the bath tub, allowing for bathing and shower drainage.
It is personal preference. Most are probably inside the tub, but for taller people or if the shower head is above the wall of the shower, it may want to be higher.
You should be able to purchase a glass shower door for about $250-$500. Check Home Depot for the best selection of glass shower doors for your walk in tub.
A "walk-in" tub/shower eliminates the need to step over the side of the tub to get in and out of the bath or shower. Older people and individuals with disabilities or injuries (as well as caregivers) find it much easier and far safer to use a walk-in tub/shower.
Yes
it has a toilet, sink, shower and tub. (if it has a shower stall and no tub it is called a 3 piece)
As long as care is taken to insure that the shower liner remains inside the tub, there should be no water leakage.
Only custon coach builders will install tub shower garden tub combos as they are not standard.