No, you don’t have to invite everyone.
You can invite members one-by-one by tapping the plus (+) icon. Once selected, a checkmark (✓) will appear to confirm the invite.
You also have the option to:
Invite all users in your favorites
Invite all suggestions: this sends invites to users in your area with shared interests
The more people you invite, the better your chances of a great meetup. The more, the merrier.