To answer all of these questions in order:

1. You can use the Canon Personas if you like, but I am allowing custom Personas to be made as well. A few custom-ones are already reserved for some of these people.

2. You'll all be starting with Weaker Personas, yes. But as you are allowed to fuse just like any fool would, that's not something too problematic. ...Also, For the record: In this RP, Throwing around Mamudoes would be something of an annoyance only. As I said, They are merely damaging elements, no different to the other four. No insta-killing properties in either of them. ...It's still be annoying and unrecommended to throw 'em around constantly though. XD

3. As there is no need for a Single Arcana for Social Links, so too are there no need to limit how many people can have personas of the same Arcanas. So long as they're not the exact same Personas, as long as the Arcana fits the character, anyone can be any arcana, regardless of who or how many are already that arcana.

....Except for the Fool, the World, and the Universe. Only one fool is allowed and I have her. The other two are absolutely forbidden...I personally think Judgment's also a nono, but we'll see about it.

EDIT: 4. You can reserve them if you like. HOWEVER, I personally would recommend you wait until the event that will give you the second Arcana choice happens.Trust me, I can almost guarantee you won't expect it.