Just ranking everything in order is the ideal rating system. And it's easy to convert to whatever poorly-chosen system someone else wants you to use. It does mean the scores for your first few ratings will fluctuate quite a bit, though!

If you added half stars and stuck to a 5-star system, there's less user surprise for functionally the same thing.

I did go back and forth on this. I just like 10 stars better. IMDB, MAL, Mangadex all have 10 stars. So it's not really uncommon. But yeah, if a lot of people feel 5 is enough, we'll just return it back to the 5 star system.

Anilist let's you switch your rating system. You can do 5 stars, 10 points, 100 points or a simple 3 points reprrsented with emojis. I quite like the idea, although I think it makes it a little more complicated to calculate ratings for all people.

You could do a simple weighting, probably adjusting for sample distributions.

I would guess that with experience and age preferences change. What's the point of a 10 star rating system if you have a 10 star rated book that you wouldn't rate the same after being ten years older?