I am talking about requirements that could count as ERP like e.g. payroll, timesheets, requests, tasks, communication, CRM/Sales, etc..
I know this depends deeply upon ones business model and needs generall advice. Currently we are using GSuite Enterprise which is nice but not an ERP system.
Timesheets: Depending on the scale, why not Google Forms, Google Sheets and/or Airtable?
CRM: Heavily depends on what type of business you have (e.g. few large customers with long sales cycle, vs. many small customers). Go with something simple (Google Sheets) if you don't know your workflow and requirements yet.
Tasks/communication: buy a copy of 'The Great CEO Within' and read it cover-to-cover. Pick something to implement. Do it. When you're done, open the book and find the next thing.
Sales: what type of business? Maybe read 'Presictable Revenue' by Aaron Ross, SPIN Selling (classic book on sales) or (if SaaS), Holloway's new book 'Founding Sales'.
ERP: not sure what you need here. Do you manufacture or sell a physical product? If so, maybe something like Netsuite? Or maybe look in Shopify's app directory to see what's popular.
Most important: document processes so that you avoid single points of failure, are prepared for rapid scaling in # employees, and can easily identify and act on opportunities to increase efficiency.
You may also find something useful in Verne Harnish's book 'Scaling Up'