Onboarding customers 1:1 is something a lot of SaaS still do. That's fine, just build it into your business model. Hire account managers, etc.

It's also fine to do things that don't scale, that's how most startups launch. It might not keep up with the pace of growth, just have a backup plan for that.

Also just saw the last question. No, probably don't charge them yearly for a product that hasn't been around for a month. We see a lot of products where the site keeps breaking down after a few months. You need a lot of trust that you're willing to commit. Many get it with a 100% money back guarantee or even 110% money back.