Rick Riordan, the author of the Percy Jackson book series and a producer on the show, has stated that his intentions are for the TV series to be long running (source):

However, fans need not worry as the producer has made it quite clear that the series will be going on for more than five seasons!

The series has already completed a first season (which was quite well reviewed), and has already been picked up for a second season. Will the current Disney+ Percy Jackson series cover all 5 books in the series before being cancelled?

If the Percy Jackson series is picked up for a season 4, which covers books 4 and 5, this Resolves YES. This market is about 5 books, not 5 seasons. If the show is canceled before this happens, this instantly Resolves NO.

This one could be a bit subjective, so I won’t bet here. I read the books as a kid and will likely be relying on the internet (Wikipedia, Reddit, articles) for clarity on what was changed. In my eyes, Season 1 fully comprehensively covered Book 1.