No, it shouldn't leak around the seal, you can usually buy new seals for
them, but maybe the seal just didn't seat quite right when you put the lid
on, try opening and reclosing it when it is hot, but don't open it if there
is pressure inside, they are great fun when you take the weight off while it
is pressurized, run cold water over the pan to cool it down quickly.  Did
the drip continue after pressure built up?  Usually a leak will emit steam
when you get pressure going.

You can cook things from the frozen state, you would have to adjust the time
for that.  It tenderizes more quickly because it cooks more quickly, really
that is the difference between pressure cooking and simmering--speed.
Because of the pressure the temperature is higher but since there is
moisture also contained there is no danger of burning the outside as there
would be with high temperatures in the oven.

You could cook a whole chicken with no problem, it doesn't matter whether
meat is cut up or whole.  You have to use it a bit to get your timing just
right for various stuff, things like meat can stand a bit of overcooking,
they will just get more tender.  Things like potatoes (I know, just an
example) will disintegrate if you cook them too long.