1. Since you started as a mage, the mp of any non-magic character will feel like it is running out fast. You will just have to get used to it and possibly wear some altiverse rings that give a little mp on them (+1k ish, it adds up).
2. Poison is quite the skill for bosses along with hide, item detector and 2 AoEs. This makes foxes a rather bakanced class for all purposes. Lions are similar in that regards with shield breaker; however you can get shield breaker on a guardian for a fox. What lions have skill wise is speed. They can land several skills in quick succession.
4. The normal attack of lions is 20*(ac-49)+gunap, and it cannot be aided by attribute. It does have the advantage of range however.
I would honestly pick a fox as they are easier to gear with ingame equips. They have close to no reliance on refining (just comp DA) and you can get an ingame headgear and mask for them. (Eyepatch and rally towel)