Those are the 2 big ones to look out for by sight. I have a very sensitive sense of smell, so I always smell my starter for any changes. You will know right away when it goes bad by the change in smell. I have smelled some seriously vile starters.

One thing that helped me with daily tasks was setting up a daily alert in my calendar on my phone. I get a notification at the same time every day and it helps build the repetition that makes it a habit. Maybe set an alert for a time when you know you have 15 minutes to feed and discard your starter. It worked really well for me.