The number of posts is like what level you are at. Here are the qualifications to create multiple Vocaloids/Utauloids.
100 posts-You can make a second Vocaloid/Utauloid.
200 posts-You can make a third Vocaloid/Utauloid.
300 posts- You can make a fourth Vocaloid/Utauloid.
You are only allowed the maximum of four Vocaloids/Utauloids unless I change my mind.
Also the number of items and songs need a certain amount of posts.
10 posts- You can make one item and song
20 posts- You can make a second item and song.
30 posts- You can make a third item and song.
I'm pretty sure you get the point now.