there is a software where i can design my own processor? i mean, simulating, mounting circuits, etc

Not long ago, I tried Logisim to learn how to make a very basic processor. I found it pretty quick graphical way to learn from and soon had a simple 8 bit processor with it's own memory, instruction decoder and ALU. (It was a bit of a hack though ) It's a standalone 5MB Java app.

If you want to go further there's Xilinx which allows you to design and simulate circuits as well as export the design to an FPGA (programmable chip). There's a number of beginner/developer boards which connect the FPGA to a number of interfacing components (buttons, LEDs, VGA controllers and so on). One thing to note is this is BIG the download is 4GB which installs to 12GB but it has a lot of tools and features.

Both are free to download and available for Win/UNIX.

Yes, look at all the emulators out there emulating 3rd party processors. vMac, BOCHS, SheepShaver, VirtualBox, etc.

You should take a look at VHDL or Verilog.
There are free simulators available for them, like GHDL or Icarus Verilog.