Her baby teeth will start falling out at about 12 to 16 weeks old.  Don't let
her bite your hands as if they're toys or she may grow up and continue to do
this is an adult; use toys instead when she starts biting.  Make sure there
is nothing on the toys that can come off and that she can swallow such as
eyes, tails, etc.  If there is, remove them.  No, the catnip toys aren't
harmful.  As she is only 13 weeks old, she should be eating her kitten food
whenever she wants.  Kittens grow extremely fast so that is why she seems
like she is getting big fast.   No, it is not bad,  it means she is growing
which is good; she will be full grown when she is a year old.  Feed her the
kitten food until she is a year old, then switch to adult.

I agree...DO NOT LET HER BITE YOUR HANDS NOW!!  I made that mistake and had
to retrain my cat to not bite/scratch at me as if I were a toy when she got
older.  She's two now and while she doesn't "attack" like she used to, I
still get bit and scratched when we're playing sometimes...and I have some
scars to prove it:)  It may seem cute now and it doesn't hurt when they're
little, but when they're adults, it hurts like hell! :)  You don't want to
have to retrain her.  Break the habit now while it's easy to get away and
just don't let her do it.
Beth

To address the weight issue, it's difficult to answer having not seen your
kitten. Best thing for your kitten is Kitten Chow or another high calorie
kitten food. Kittens need kibble AND wet food to make sure they get enough
calories and a varied diet. I used to put a bowl of kibble out with a couple
of tablespoons of wet food mixed in. It made the kibble tasty and they would
get enough moisture along with enough calories. If you are concerned about
weight gain just go to the vet, usually having a cat simply checked out is a
reasonable cost. Only a vet could answer your weight question since he's the
medical expert and he can examine your kitten.

When my kittens would teethe, I would make sure to play with them everyday
with toys that were soft yet firm so they could gnaw on the toys and have
fun at the same time. Yes, they teethe similarly to babies. I imagine it
would be painful whenever any animal had teeth cutting in through their
gums. If you want to get good chewing toys, don't just look in the cat toys,
try out the dog toy section as well. There are smaller toys available that
are good for cats too. Just remember that kittens' mouths are pretty small.
Smaller rope toys in the dog section are appropriate. And to add some
comfort, you can put a couple of toys in the freezer to make them cool and
it will help soothe their gums when they gnaw on them.

As for overdosing on catnip... no, catnip is not toxic to cats. They don't
overdose and become ill. What will happen if they are "overexposed" is the
catnip won't affect them as much... they become immune to it to some degree.
Catnip toys will eventually lose their potency and it is normal for a cat to
not react as strongly to a toy that once drove them nuts. I prefer catnip
toys that have refillable pockets to them so you can put fresh catnip inside
whenever the potency dissipates. I have read several webpages about catnip
and asked my vet. What seems best is to buy little tubs of catnip and keep
it fesh longer by putting it in the freezer or refrigerator and only using
catnip every once in awhile like a special treat, not as an every day thing.
This ensures that your cat will react to the catnip every time it is
introduced and not become "immune" to it.

Plus, not every cat reacts to catnip the same way, some eventually stop
reacting to catnip at all and that's normal. Many cats never react to
catnip. That's normal.

Also, if you ever simply give your cat some catnip straight from a
container, it's normal for them to eat it.

There are many many websites to investigate for tips and hints about cats
and rearing them. Go surfing :)
Good luck with your kitten!