Spells can give you familiars too. Familiars and animal companions can border on overpowered, especially at low levels when a Wolf can be stronger than an entire low level party.
Considering a familiar is at most 10% of its caster, and an average wolf is 40 kg, I'd like to meet the 400 kg mage... :p
1) First, remember the weight limit (well, okay, mass limit but I'd assume a world with a gravity equals to 1G
). With the exception of spells from "
Familiar's Law", most familiars would be the size and weight of an average housecat... therefore not that dangerous.
2) However, first and foremost, I think you have to make sure the character understands that his familiar is more than a pet: it's one with which he's
attuned! Sure, he can "control the familiar and view the world through its senses" but it is foremost a companion that shall never betray him, shall always be on his side, shall always be able to understand his feelings, shall always and unconditionally love him, with which he can freely communicate, etc., in other words, with which he shares a bond that no one else would ever share. Just consider: IRL, people have pets, animals with which they cannot communicate (though they'd say otherwise), nor any of the above (though they'd say otherwise). How do you think these people react at even the idea of their pet being injured?
Sure, the pet would be willing to endanger itself to protect its master, and the master may allow it to do so, but, above all, each would
care for each other, and do not want to the other to take risks.
As such, my suggestion would be to play the familiar as an actual NPC (with limited/basic intelligence but...) rather than a mere animal.
3) As far as I'm concerned, aside from rules allowing familiars to progress (in many stats: level, speed, base rate, CON, and IQ) and their master to similarly gains stuff (bonus to skills, hit points and DB), I have such masters to interact with their familiars as with their best friend, confidant or even soulmate. Meaning I don't have many characters with familiars, since each is an individual NPC, with its stats, personality, etc., because I don't want to unnecessarily add NPCs. :p
4) At last, food and climate. Most animals aren't omnivorous, nor able to survive long outside of their living climate. Yes, a poisonous snake is interesting to have as a familiar, but it won't often be active as soon as cold comes...