1a.Do NOT wait for the oil life monitor to hit 0% before changing the motor oil.
Even if you do not disable or delete v4 mode, the more often you change your oil and filter, the longer the variable mode lifters will last before they force you to replace them.
I'd suggest changing the oil and filter no later than every 4000miles.
If the vast majority of your miles are lazy highway miles in clean air, maybe 4500 miles?
(Along the same line of reasoning, changing the ATF and ATF filter more often than recommended by GM will help the transmission last longer too. I'd recommend no further than every 35000 miles, or less.)
1b. If you cand find the larger oil filter for your engine, the longer one's extra filtration capacity will make longer intervals betwen oil changes make more sense.
2. If V4 mode has not been disabled, the best investment for the longevity of your engine AND transmission, is disabling V4 mode.
If you are sure you're gonna keep them forever, save up and delete V4 mode hardware when your finances are well shored and buttressed.
3. although reprogramming the ecm & tcm is not cheap, the improvments in drivability, durability, and longevity will pay off over time.