Like others are saying, proceed with caution. From your posts, it seems
like you don't have a full understanding of what's going on, and amateur
electrical work can be dangerous. But, you're doing the right thing by
researching the subject before acting, and you may learn enough to feel
comfortable with the project. Definitely research local codes, and
before you do anything, find out what the inspection requirements are.
You may well find that this is something worth bringing in a pro for.
That all said, this is my own amateur-with-some-rewiring-experience
The "two pole breaker" you refer to is actually a pair of 120 V breakers
physically linked to trip together. The breakers are on opposite phases
of the power, so that the potential between them is 240 V (or whatever
it comes to in your neck of the woods, typically anywhere between 208-
So, considering the hot leads only, there wouldn't be a problem
replacing the two linked breakers with 2 separate 15 or 20 Amp circuits,
as 8-gauge wire can handle plenty of Amps.
But, you mentioned it's a 3-wire circuit, meaning two hot wires plus a
single neutral (plus a ground, right?). So, if you have separate
circuits, you'll need to pull another neutral and another ground wire,
so that each of the two "new" circuits will have an independent neutral
and ground dedicated to it. In practice it's often more practical to
just abandon the old wiring and pull fresh 12-gauge wire to the desired
locations. Leave the old wire in the walls; maybe one day it will come
In my experience, adding a 20 A circuit is a snap if you have the
ability / access to pull the wire to where it's needed. Read up on local
requirements and get a book about appropriate wiring practices.
Good luck. Let us know how it goes.