Each book has a standalone ending, so you can read them in any order. If you do want to read more, and I hope you do, there is a larger arc for each cycle, and a larger meta-narrative across cycles that will become apparent later.

At the moment you don't have much choice in where to start, as only The Year Before The End and Galaxy Bound are out, but you're not committing to "having to" follow the series through at any point.

Book 3 will be out autumn 2022, and the Sovereign Earth Cycle is due to complete publication in 2023-2024.

Sovereign Earth Cycle