Yeah, so you HAVE to measure what is working and what isn't working. There are some things you just need to go quickly and sign up for.
A good approach here may be to choose Google analytics plus at least one of the honorable mentions below. You probably can't go wrong, so as a scrappy entrepreneur maybe choose the cheapest or the one who is willing to partner with you and give you their service for a year on credit. I used Google Analytics + Vercel last go-round.
This is easy, just go do it. Almost every provider or web host like Wix or Squarespace will support Google Analytics so go sign up for it and set up your code. If you are using NextJS or some other Low-code solution chances are it also supports GA. Make sure to set up a separate property for each website, like if you have a Dev / QA / Production setup you should have a property per environment.
If you chose to deploy to Vercel, their page load analytics are super cool. They can show you all the same things as Google analytics plus information about pain-level your users are experiencing by slow page load times. This one isn't free, but for the cost it's pretty easy to integrate and has lots of value.
I haven't used any of these but I've either read awesome things about them, or analyzed them or for one reason or another chose to use something else.
This looks super easy to use like Google Analytics but it ain't google.
If you hate the idea of Google or some other provider storing your analytics, you can just host it yourself.
This is one of the hot mass-market analytics platforms for user-journeys and all that. This is pretty full-featured and can help you learn a ton about your users if you can afford a system like this.
This is a great way to capture data and send custom events from your application to track your user's engagement. I highly recommend this tool. Very developer-friendly and easy to use. I've had mixed results with product managers willingness to build dashboards and instrumentation, but hey product managers...
Another up-and-coming tool that seems folks like to talk about. I've yet to have a chance to dig in hard here but it's probably worth a look if you can get a good deal on the paid version. You likely would choose this or MixPanel or Amplitude, not all 3.
This is absolutely amazing, and if you have some serious user engagement but are struggling to maximize conversions in a funnel, or want to see more granularly where you are engaging your users, consider this tool. It's super easy to plugin to your application for your engineers and it can provide record/playback big-brother oversight into what your users are doing. I also recall that it can obscure certain fields if really necessary.