Or is this going to overtrain? I like some upper body HIIT, and I just figure I can do that in between lower body HIIT, or am I just going to overtrain the heck out of my body? Anyone with any advice for me...thanks!
You're not necessarily going to overtrain, but it's unclear if you'll make more gains than if you just did it 3 times a week. Why would you only do upper body weights? You need to do upper and lower.
It's great that you're able to bike, run, swim, and row. You should try HIIT 3 days a week and lifting on two other days, and this also leaves you with two days of rest. I think this would be best, and is at least the proper place to start, and you can always add on more in the future, but I wouldn't recommend doing anything else on your weight lifting days or having less rest.