I've only been on Tapas since July, so not a long time.
Anyway, regarding popularity and income - 25 subscribers, $0.00.
I feel pretty successful though because popularity and income were not the reasons I started my comic. I started it for one reason - to improve my art skills, and I published it on Tapas for two reasons - to keep myself accountable and force myself not to be too perfectionist by setting deadlines for myself.
Success is easy to measure if you know what your goal is. I had/have one goal - to improve - and I have improved a lot. 