I post minimum of 3 images, up to 6. Minimum 2 hours between posts. I post that often, becuase I "teach" my followers that they will see 3-6 images every day, because when I start to receive up to 6 shoutout orders, they won't start to unfollow just because I post often. Now you can say " well, you can post once for higher shout price and you will have the same ammount of revenue for less work ". I have tested and to be honest it's not like that. I earn more money if I put lower price. Also every new follower can see how often I post and decide for himslef weather he want's to follow me or not. Normally instagram users spend 10-15 min every day, i'm talking about normal users ( not marketers, addicted people, etc ), So posting up to 6 images pull a lot more attention and eyeballs on my account. If you build your account from begining and post 3 - 6 times a day, people will get used to your posting habbits. If you build your account posting once a day and after that you start posting more than that ( because you have people asking for shoutouts ) you will see how people start to complain about this "spam" and many will unfollow, just because you have "teached" them that you post once. Anyway...
Good luck to all!