What everyone said, with this addition:
If you have a lot of background description that you just really feel is important, make a separate choice link leading to a page with the excessive description and then have a loop choice back to the main story.
Focus the meat of the story on the regular pages and if the reader wants to they can always click the extra description choice.
As far as choices, try not to have too many linear single choice pages in a row. Really anything more than three in a row and you’re starting to push into regular non CYOA territory, unless there is a really good reason for doing it that way (Scripting or something).
Personally, I think you can get away with the two choice minimum as long as you’re writing everything well. I guess if you want to be safe, have three or four choices, but again that’s more pages you have to flesh out for each choice.