They're fun, but I'm beginning to think that the computers on my bikes are mostly unnecessary. About the only practical thing that they're good for is to keep track of mileage for scheduling maintenance. But, with chain checking tools like rohmen mentioned (and the variety of conditions that can make some chains wear faster than others), and every other part's tendency to make weird noises when it needs attention, even mileage numbers don't always apply.

Get some stuff for cleaning & lubrication, and you should be good to go.

Once you get competent at making adjustments, you'll be able to keep the bike running well, and you'll know for sure when something actually breaks. I did have a shifter crap out on my older MTB, but I only took it in after I couldn't get it to shift right with any possible adjustment I could make.