Where can I learn about integrating services with my app?

I have a really early stage idea/app. It's basically a WYSIWYG editor for internal purposes. The goal is to make it simpler to bust out simple websites for clients and the plan is to make it available to clients to use if I can get the UI intuitive enough. I'm confident I can get this done, but then I thought, "Why stop there? What if that works out and I want to scale to everyday people? How would I deploy their freshly designed website to something like Vercel without them knowing what Vercel was? How can I get form submissions emailed to them? Use our own mail provider account or can I create their own account?"

So far, we've been setting up Netlify, GitHub, Mailgun, etc. accounts manually and adding API keys where needed. How would I get accounts created with certain services providers programmatically? Is it normal to contact these providers for specific instructions?

I'm wondering how Netlify got things started with letting users manage DNS or their Forms service. I noticed Gatsby Cloud partnered with Fastly for their hosting. Would big companies even respond to me?

And most importantly, would it even be worth it to someone with limited resources?

At the very minimum, my goal is to have a user-friendly React app that has a "Deploy to Netlify" and/or "Deploy to Vercel" button, but I'd appreciate it if someone could point me in the right direction to learn about this.