I don't know if my experience will help but I've been working on a long-form project for about 9+ years and it's about 1/3-1/4th of the way done at about 450 pages. If you look at a lot of long-form comics like Old Boy or Akira that's honestly about the same length. It's just good to have perspective on length going in, that sometimes a story just needs a bit longer to tell.
City of Cards is not my first comic, it's story I sat on for about five years before deciding to commit to. I spent a year of art school kicking my butt to get better at art/comics, did a test chapter to see if after doing 20+ pages I was still invested in the story, and had lots of help with peers and advisors to make sure my foundation was strong enough to carry for as long as I knew it would take. I still had a lot to learn but I had done my best, and that's all you can do.
This is all to say, if you really invest yourself in the story and the idea, that will help you weather whatever happens. Find the people who have your back and believe in your work and listen to them when you start to doubt yourself.
I say be wary of falling into the trap of page by page reader gratification if you want to tell something that lasts. It might be better to update in larger chunks, whatever works for you. I agree with the people that say arcs help, they can give you short term goals that help you feel accomplished while you're aiming for the bigger goal. Goals are important! They keep you motivated.
Here's some positives as well aside from reader numbers: despite not having gotten a huge audience, I've been able to successfully kickstart a printing of my first 400 pages, I've made a lot of friends in the comics community, and my skills have improved enough that I'm seriously looking into pitching other projects to publishers. From the start I wanted to see my work in print, I do my best to not let numbers discourage me from getting results.
It's up to you what you want. If it's a story you really, really care about it might not be easy to put something out that you know will take a long time for payoff, but it's not all bleak. Additionally: if you decide a couple hundred pages in you can't keep going, you can decide to do something else. You'll have the skills of a couple hundred pages under your belt and that will carry on to whatever you do next.
Your first project doesn't need to be your only project, but if you want to tell a big story you're also absolutely allowed to be as excited and obsessed with telling it as you want to be. Good luck, go for what you want, whatever that ends up being.