Well logisim is dead, but evolution is a fork and then there's Digital https://github.com/hneemann/Digital which is I think a reimplementation of Logism's concepts?
I also hand designed a custom 16 bit CPU in logisim, because I was struggling to understand Nand2Tetris's HDL as well as I liked, and also because I stopped following the curriculum to go my own way.
Logisim has a few hang ups, starting with a rather low upper bound on clock speed, completely single threaded simulation, and no process for PLL or similar clock multiplying strategies so if you want to do internal processor management or microcode based implementations, you will be stuck with an even lower fraction of that clock speed. The UI is slightly clunky by modern standards, debugging complicated circuits is less than fun, and the file format is less than great if you want to do anything more than no version control and only touching it with logisim
I also hand designed a custom 16 bit CPU in logisim, because I was struggling to understand Nand2Tetris's HDL as well as I liked, and also because I stopped following the curriculum to go my own way. Logisim has a few hang ups, starting with a rather low upper bound on clock speed, completely single threaded simulation, and no process for PLL or similar clock multiplying strategies so if you want to do internal processor management or microcode based implementations, you will be stuck with an even lower fraction of that clock speed. The UI is slightly clunky by modern standards, debugging complicated circuits is less than fun, and the file format is less than great if you want to do anything more than no version control and only touching it with logisim