It's all about getting off the smokes. Don't worry about the numbers.
Listen to swedishfish and don't worry. As you transition, your body won't be a bit shy about letting you know when you need to crank the nicotine up or tamp it down.
Because I puff so constantly, I thought that meant I should use lower numbers. However, various events (recounted in various places around here in stultifying and exhaustive detail) taught me that no, I needed to pump it up to 36 - and my Marlboro consumption took a very respectable nosedive almost overnight.
But that does NOT mean that you need to do that. We're all unique, and finding our own special nicotine nook is just part of the process.
Sadly, there's no magic formula, unless you count trial and error as magic.
When we puff our e-cigarettes, our bodies don't receive and process the nicotine at the same rate, or in the same way as when we smoke tobacco ones. (You can read all about that in the ECF library, etc if your brain understands such things. Mine doesn't. It just accepts them and puffs on).