I'm not at expert when it comes to ipe but I will try to answer your questions to the best of my ability. When you go to order your lumber you might want to double check my answers.
1. As far as I know there are no unusual health or safety issues with ipe. It is wood so there is always a chance that it will splinter and could cause splinters. There are a couple building methods you should know about. If you need to use screws on it you will need to drill the holes. If you dont there is a chance the board will split. I dont recommend using screws on the deck though. The other thing to know about ipe is that it comes in two styles. One style has a slot along both edges while the other style does not. The slot is made to accept an ipe clip (hidden fastener). I recommend using the ipe clip. the slotted boards can be used on the main deck while the unslotted boards can be used on the stairs.
2. There are a couple of changes you will need to make for this deck. First your deck height is over 30 inches. Therefor you will need to use diagonal bracing to keep your deck sturdy. The following link will explain this better.
deckplans.com/deck-height-over-30
The other change you will need to make dependent on on the board length. Ipe comes in random 2 foot lengths. The shortest length being 6 feet and the longest 20 feet. Some companies will work with you to get the board lengths that you need or want. For others its whatever they have in stock. You might need to change the deck design so the support boards are 2 feet on center. I do not recommend putting the support boards any farther than 2 feet on center.
3. Maybe. Its possible to build the entire deck and put the handrail on later if you would to bolt the handrail to the outside of the deck. If you would like to have the handrail on the inside of the fascia board then, as a minimum, you will need to put the posts up and build the deck around them.
4. It is possible to have a cutout for the faucet but you might want to have an access panel instead
Hope this is enough to get you started.
Deckman