It's great that you're confident in your writing! I think you should use that as you go forward. You won't know how people will receive it until it's out there to be received, and then I think you need to trust yourself to learn and respond to whatever reaction you get. You're always growing and adapting after all. Give yourself permission to do that, don't expect things to be perfect.
A nice cover can only help. Free stock and a little creativity can go a long way. I also think past boards have referenced a website that's helpful for making free covers? I'll see if I can look it up. Else wise commissions are a very good way to get something tailored to what you want, plus it supports the art community. Always good to make some connections there. =)
What helps my anxiety is focusing on the idea that my comic is for me, that it is fundamentally a project intended to make me happy, and everything else (like subs, likes, comments) is lovely but totally secondary. I still take it very seriously, but this thought process helps me keep a mental buffer. I still have bad days, but it has really helped, and my comic does make me very happy, which makes me more productive anyway!
You'll have to think about what works for you. Perhaps writing large batches of updates ahead of time, that way you won't stress about the schedule, nor have to fret about writing the immediate update. Plus planning breaks/hiatuses (I do mid chapter and end of chapter breaks) can be helpful.
Maybe start with a shorter story, something that would be low stress for you, and go on to bigger projects as you get comfortable. It depends a lot on what you want to do though! But approach things from whatever place of mental strength you can.
And very important: do not obsess about stats!