Basic Questions for Starting Pet'ers

Anyway, I'll like to answer a few of your questions.

What pets are best suited to what roles?

-Every pet have three modes. Fight, Protect and Relax. In fight, the pet's speed is slightly increased and will attack the enemy.
In protect, the pet act as a tank. It takes half the damage you get. Like if you get 200 damage, you and the pet will get 100 damage each instead.
In relax, the pet won't fight but it will still heal you and their natural recovery rate increases. Take in mind that your pet will receive damage from the enemy if attacked.

Depending on the situation, your class and how you have trained your pet, you might switch between the modes. Personally, I usually set my pet on protect when I fight bosses who are tougher than me and on fight mode for ones which are easy and while farming. And I use relax when I am resting and my pet has lost a lot of HP.

What pets supplement what classes?

-Well, I only got 3 colons has pets. My pets have the abilities to use mana wave and heal aside from attacking. Maybe other pets have different skills? I cannot say for sure.
Anyway, I think every pet will come in handy to every class depending on their needs. Like if they want their pet to be a tank, then they should train their pets for VIT. For healing, DEX and INT.
Not to mention you can solo around with a pet since they can revive you if you get KO'd. Though the pet may end up being KO'd in the process. But this really comes in handy.