Yes! You can always add more tiers at any time.
If you want, you can launch with only a free tier! Then you can add a paid tier(s) whenever you feel comfortable!
One thing to keep in mind is that if you raise the price of a tier from $5/mo to $10/mo, anyone who signed up at the $5 price will be grandfathered into that price for life.
Some artists will keep the $5 tier and just add another tier at $10 which the $5 tier can upgrade to - but it is completely up to you!