Not only can you have book 1.00
you can fill in between

book 1.50 is valid
next thing for you to look at is the Preferences for Save and Send to device. This affects naming on folder
only based readers.
setting: {series}/{series_index}-{title}
will pre-pend the book number onto the title, so they sort in book order in the readers title list
eg.
Homecoming_saga/1-The Memory of Earth