For a new early stage startup, what is the most recommended and feasible platform to establish e-mails, shared files and collaboration tools?
The answer is always going to be "it depends." It depends on how much money you have to spend, what your requirements are, the number of users that will be involved, etc. G-Suite, Microsoft 365, and a bunch of other SaaS office software suites are available at relatively low and similar costs. Without a specific set of requirements, no one can help match you with the "best" option.