Tooling advice for a small distributed national team

Hi there we're a small startup with very different background. I am an healthcare subject matter expert with some AI/Data Science/python scripting experience, a very senior backend programmer on NLP, Knowledge Graphs and two juniors, a frontend dev and a backend/infra person.

We'll be hopefully embarking on some tight schedule full stack dev in the next months after developing proof of concepts which will become part of the solution.

The main components are Stanford's NLP pipelines, Protege/Apache JENA SPARQL endpoints, Redis key/value, plotly/dash/cytoscape visualizations / React.

I'd love to tap into your experience around tooling to efficiently support such a team's development keeping good control of what needs to be done, by whom, issues, testing maybe CT/CI …

So far we've been using Github as our repo and whatsapp as our "chat", some Google features such as Drive and Calendar.

In the past have used Slack which I think would be a lot better than whatsapp, also have used Trello for a very lean kanban. Very ignorant about testing and integration.

Costs are a very important issue until we'll get some consistent business.

On the business side of things keeping track of what opportunities are in the pipeline, what need to be done, expected revenue etc could become more complex in the future, so far maybe a Trello KanBan might suffice ???

Thank you from my heart for any good suggestions.