There is a "consulting" fee for the hosting service that depends on the duration of the party. We will discuss the party themes and what wines to choose, which will then be purchased by the customer. The fee depends on the size of the party and whether it is online or in-person. Online parties are a bit more economical because there is less coordination, travel, etc.
10-12 for an in-person party is a manageable size, but it is really up to you. A bottle of wine will allow for about 16 typical ~1.5oz pours (give or take). If you have more than 14 people or so, you may need two bottles of each wine to ensure that each guest gets enough, not to mention, guests may want to revisit the wines that they like.
Online parties can be as big as you like!