Something I would add: LTSpice! Free (except for your time), but once you build up a muscle memory you find issues with parts before you order them. Just recently I used this to discover that I had missed an opamps minimum signal input voltage was V- + 2V when I was trying to amplify a 0-2.5V signal with a unipolar power supply. Playing in SPICE taught me that I need rail-to-rail opamps if I want to work with low voltages and unipolar supplies.