Is too much of my home connected to one circuit breaker?
There's really no substitute for painstakingly mapping your house, going to every outlet (by which I mean "point of use", including hardwired loads) and figuring out which breaker serves it.  I have done this A LOT.  It helps to own a bunch of dollar store nightlights, strings of Christmas lights, whatever you can plug into a receptacle.  If I were king, it would be required to be marked on the outside or inside of every outlet.

If you're exceptionally clever, you can put a card with each breaker number on it, at each outlet.  Turn off half the breakers, go through and if it has lost power, cross off the still-on breakers, and vice versa.  Turn off a different half and repeat.  Soon you narrow it down to 1 possibility. 

After you've done the mapping, you can think about the likely route of the wires, and ways to access that wiring to add "home runs" back to the box.  For instance if your wiring goes Panel-A-B-C-D-E-F-G-H-I-J-K-L, and you can route from point I to the panel, then you run two 12/2 cables there, feed I-L with one cable, E-H with the other cable, and in box D and E, disconnect the cable that interconnects them.  So now your segments are Panel-A-B-C-D   E-F-G-H-Panel  Panel-I-J-K-L.  

But this will only be the result of your particular mapping, and the logistics of pulling cable in your particular home.  As such we cannot begin to advise you. 



** Using the formal definition of "outlet", anyplace a load connects, including hardwired loads like lamps and fans.