Really nice to see! Since the past several years I'm working on a text based ERP system (that of course do invoicing as well). Nice to see that there's a demand!
I'm having same considarations, but strugling with finding the best feature-set
Right now I've: Accounting, CRM, Email, Products, Invoices, Quotes, Password manager, Tickets/Todos, Projects and basic IoT device monitoring and a static webpage generator. Most modules let the user add their own fields to a module so you can make if fit your needs.
Apart from this there's also lua support for reacting to events. Upcoming is webshop capabilities and cronjobs.
Feature sets are hard. But I'm prioritizing things my customers wants and what I need.