Set up Google Analytics (GA4) for the company

We are an ed-tech called Goseeko, targeting tier2&3 colleges in India. We are a startup, and we appreciate it if you sound out your perspectives and give suggestions that fit the project. Specifically, we need data from the existing setting to be migrated to the GA4 setup. We should also be able to use GTM as our platform to manage tags. New GA setup has to have both website and app data coming in while the current setup is for the website. The final setup has to be as seamless as possible.
Ideally, you should have already set up a GA before.
Pay can be further discussed.