Huh? What prevents you from installing them "all at once"? The downside is obviously a long stretch of no sun, and for Europe winter being both low solar production and high energy demand due to heating which the soon-to-be-cheap grid scale batteries don’t really fix. The logistics of PV don’t seem difficult though - it seems by far the easiest of the power generation methods, even if the synchronization can get a bit tricky in a large grid.

Because manufacturing isn't there to do everything at once. You install say 50gw per year, each year. In 30y you need to replace first 50gw batch and so on

Any real system will also have backups and emergency reserves.

Lean more on them as you solve the supply chain issue.

No need to make a mountain out of a molehill.