Do all 130 of Bella's pets propagate across ALL my alts (I think I have something like 20 alts in total)?
Imagine, if you will, something like the guild bank, but that bank is only accessible to your characters on a particular battle.net login. It doesn't matter what server your characters are on, or even if they're on separate wow licenses as long as they're under a single battle.net account. Now imagine that this bank only holds minipets. Now imagine that this bank that is accessible to all your characters has 500 slots. The only caveat is that you can't put more than 3 of any particular item in this bank.
Get the idea?
In other words, Bella and all of your other 19 toons will all have access to the same pets.
And if 3 of my alts "cage" the same pet (say, the crimson whelpling), does that mean that Bella loses the pet?
If Bella has a Crimson Whelpling, then when you log into Bella the pet journal will now have a Crimson Whelpling in it, as well as all of Bella's other pets.
When you log into another character, all of that character's pets will go into the journal as well.
So say you have a toon xBellax that has a Crimson whelpling too and 5 other pets that Bella has, but she also has a Crimson Lasher that Bella doesn't, . xBellax will now see a pet journal with all of Bella's pets, plus a crimson lasher and a second Crimson Whelpling and each of the 5 pets that Bella had (assuming none were unique pets).
When you log back into Bella, you'll see the same thing. All the pets you had before, plus the Crimson Lasher and a second of the Crimson Whelpling and the 5 other pets.
When you log into a third character, that character's pets will also be added into the journal. And so on as you log in each character.
I'm afraid that I'm going to mess up and screw myself out of my 130 pets (I'm working towards the pet achievement!).
You're not a rabid collector like me, so you won't have the same problems.
My problem, using the the Crimson Whelpling, is that Tiggindy, Tiggandy, Mirai, Zottie, Mitrian, Koyomi, Rauni, Ambelsa, Rovina, Miari, Sachrissa, Senua, Asheley, Squeances, Gummiberry and Lindesfarne all have one. Huh, I guess that's 16 and not 15...
Anywho, If I log in Tiggindy, Rovina and Mirai, I'll now have 3 Crimson Whelplings in my pet journal. If I then log in Rauni, I'll still only have 3 Crimson Whelplings in the pet journal, so I've basically lost one of my whelplings.