Hello, Tim, and welcome to SRP. There are no simple, definitive answers to your questions. But I strongly suggest that you read these two documents:

  1. Frequently Asked Questions - Straight Razor Place Wiki
  2. Straight Razor Place Wiki:Books/Beginners Guide - Straight Razor Place Wiki

The numbers describe the width of the blade, cf. The straight razor - Straight Razor Place Wiki.

Good luck,
Robin