1. Can't Say Exactly, it's a lot though.
2. There was a thread for this, not sure what it required. How to able to see party members TP bar. (PC only) : ffxiv
3. Personally when the tank dies and you're first on threat. There are mechanics like Divebombs and Earthshakers that it can avoid. But you'll be surprised by how much it doesn't "dodge perfectly." Usually if it's significant enough you'll be informed that you can do so.
4. Yes
5. Warriors and Paladins are the only other slashers. DRK will be too.
6. You'll want to use the frontal high damage in short situations between phases if at all. You'll want to use the 10% dmg vuln almost always instead. The best way to use it is casting the Mudras to allow its usage, then prepping a Dancing Edge rotation, dropping DE, Blood for Blood, then using trick attack. You'll probably want to reapply your dots at this point in the rotation as well.
7. Yes, you should wait til you use an ability to cast the Ninjutsu so that it utilizes the GCD window. If you do anything after selecting the mudras other than casting the Ninjutsu it will fail. You'll learn to wait til it casts or pressing it twice because sometimes the server will cough, the Ninjutsu will appear to cast but it's too late you've already pressed something else and now the rabbit laughs at you.
8. Yes, I believe so. You'll probably want to save kassatsu for latency ninjutsu mistakes but as you're more comfortable with ninja, Ideally you'll be using it in between trick attack cooldowns for a crit Raiton.
9. Not sure. Best way to test would be to auto attack a dumby and slowly cast mudras. I don't see why it would stop you since they're instant. You can even cast them while sliding during Leviathon Extreme.
10. None.
11. Yes.
12. I'd say it's flavor, I can't think of anything during a fight that would be fall damage. I'm sure if there was they'd find a way to make it hurt you just as much as everyone else to avoid all ninja DPS for a specific encounter.
13. I agree with you. It should be shorter. I'm sure they looked at the damage output and timed it according to balance.
14. I agree with you again. Maybe it's to reduce the number of APMs weighing on a player. It needs to be shorter.
15. There will be times and situations in which you'll use it still. Such as, Leviathon Ex when casting Raiton on the tail will have it reflected in your face. Or when Mudra lag is extremely bad and you want to avoid waiting a full second between mudras. The damage isn't that much less but taking 3 seconds to cast Raiton instead will make it the superior option.

I really wish Fuma Shuriken kept being used primarily. I looooove its range and animation. Plus it's so quick to cast.

It would be nice if instead of rabbit all failed mudras would default to it. But I do appreciate that failure mechanic as well. Now if only latency wasn't such a massive issue and ninjutsu wouldn't fake out when being cast too often.