I'm currently building an almost identical setup! I'm using Studio One to run my tracks, with the tracks going out on USB sends 1/2, click on USB send 3, and cues on USB send 4. On the mixer, I've assigned those USB sends to four mixer channels.
To get the tracks to FoH, I'm using the main mix, but you could use any aux. I just have everything but tracks muted in the main mix.
As for extra stuff, I found with my previous IEM rack that having all the connections on the front of the rack is really nice, so I soldered up a mini patchbay to get the plugs on the back of the mixer to the front. I also used a bit of velcro cable wrap to store a screwdriver inside the rack - it came in handy many times! If you plan on letting your bandmates mix via WiFi, including a mini travel router can be handy, but you'll want to keep it away from the wireless for sure. Most routers will let you set the TX power, so reducing that can be helpful to avoid interference
I've never personally had a computer crash during a show, but just about every YT tutorial on backtracks suggests having a backup option available. I'm planning on exporting a version of our set with the tracks panned hard left and the click panned hard right, and having it on a phone. The phone is plugged into two more mixer channels. The left channel with the now mono tracks goes out the same line as the regular tracks, and the right channel with the backup click is mixed into our ears.
Hope you have as much fun setting up your system as I'm having over here setting up mine!
R