Spreadsheets used to be the way it was done, until Carta came along. So, sure, it's possible. I suspect that if/when you raise from professional investors, they're going to want you to pick a SaaS solution. Probably also a good idea if you plan to hire. If I'm taking a job, I don't want my employer cheaping out on managing my equity.

(I am not an expert. I have been a founder, but my startup did not make it far enough to have this concern. I have also been on the leadership team of a company, but equity management was outside my concern.)

Startups should use cap table management software like Eqvista for accuracy and efficiency. It simplifies equity management, reduces errors, and scales as your company grows, unlike spreadsheets. While the initial setup may take time, the long-term benefits far outweigh the challenges.