Hi Lottiefla!
Thanks for asking!
to answer your questions:
Can we use any one's designs?
YeS!
Are links to kits allowed?
NO. Links to kits or sites are not allowed 
you may use the designer name and site like this:
'kit name by Fabu Designer's Name at something or other store'
NO .com please.
Is there a size or number limit?
600 pixels wide or less and under 125K