Finance: QuickBooks
Payments: Stripe, but I plan to add Bitcoin support (most of the work is already done, its just using it is a major liability)
Marketing: Mailchimp works pretty well, I have a self hosted Jekyll website too. I also have a public Telegram group that anybody can join, but few have so far
Communication: Mostly Slack
Social: I don't really network within my field. There is no hardware or physical component to what I do, and I work from my house most of the time.
I do self host things like Git, CICD, etc, and it wasn't really worth the trouble. When this scales out to beyond say ten people I'll definitely migrate to a SaaS stack. The biggest pain point with self hosting was choosing Drone CI for the CICD. That has been the most fragile part of the setup by a land slide.