Never built my own but hear me out, I have years of experience with a Flashforge Dreamer, which falls under #1. I personally found the second nozzle a hinderance to even 1 color prints since it would often bump into partial prints if/when the printed layer height is raised even slightly higher than it should be. The common workaround to reduce that from happening is by raising the nozzle about 0.5-1mm away from the bed, but of course that then causes additional issues.

Don’t get me wrong, the Dreamer’s a helluva machine, but considering how rarely I had something I want to print (or could print) in 2 colors, I found the additional nozzle a waste. Eventually I raised up the hot end entirely, conceding it wasn’t worth the trouble, and I also removed the second stepper motor entirely to reduce weight & increase fidelity.

Don’t let me keep you from tinkering if your mind’s set on building one, but if reliability is the name of the game, I’d look for an existing solution like a kit or predefined plans and build your own design off of that.