Now I am not a 100% certain on what your startup would be producing, but I am assuming based on a lot of in-the-wild examples I have seen in my past couple years as an engineer, and can recommend you a general stack that should work fine for you at minimal cost (bar HIPAA, I don't know much about it, and someone else, more experienced would answer it better):

Cloud: Cloud costs are more or less the same throughout the major players, and since I prefer things to be developer friendly, I would prefer using Microsoft Azure to handle your architecture. Azure provides a lot of services out of the box, with good, developer friendly SDKs and documentation, which would mean less hassle for you to learn (or train) any further joinees.
Git: Use GitLab, because you can use it to have an on-prem deployment over on your Azure stack, and can easily integrate CI/CD tools to it, since it is open source and has a plethora of integrations with major CI/CD tools
Tasks Management: Use Azure ADO Boards, provided through your Azure subscription
Programming Language: I have found Spring Boot (Java) + Angular (TypeScript) to be a combination that just works, given there's almost an infinite amount of free documentation available for them to create, test and deploy RESTful microservices, but MERN/MEAN is also amazing for any startup. You can use MariaDB, PostgreSQL, MongoDB etc. as your database, since Azure has good support for all of them, but choosing between SQL/NoSQL is dependent on how you are structuring and storing your data, and I'd recommend doing an architecture review of it first.
HIPAA: sorry, no idea!
CI/CD: Azure provides ADO Pipelines, GitLab also has its own CI/CD tools, and also allows integration with industry standard tools like Jenkins, Hudson etc.
Testing Suites: Depends on what stack you would be choosing, but then again, industry standards are JMeter, Postman etc.
IDEs: I have always found IDEs to be a "developer preference". I personally use both Eclipse and Visual Studio Code, one for Java and the other for Python, Node.js, YAML, Bash scripting etc. But, Visual Studio Code has a plethora of extensions that make it a fully-fledged IDE.

Palaash's Stack