Spend a few days identifying problems people pay for, particularly easy problems that you can build yourself. The key is that the solution has to be fairly easy to build since you're not comfortable full-stack. Once you've chose a solution that already makes money solving a problem, build the same solution but position it for either a niche market or make a better product than competitors.

I would at minimum leverage bootstrap or semantic ui as your ui. Otherwise, hire someone to do the web interface for you.