a. If you aren't putting data into an analytical database, it's the most important thing you can do. It'll take a while. It'll probably be more expensive than you want, but it will absolutely change your business.
b.Give business users a tool that empowers them to answer questions on their own, as much as you can.
c. Then define success metrics, and success metrics should absolutely focus on engagement and retention. Go for the shallow, low-hanging fruit, but also go deep. It really depends, just be smart about it