is it ok in the game to pay people to send you stickers for your collection?

Sure, but there are also plenty of people who will do it just to help out. If you check out the Achievement forum, there are several different stickering threads.

I'm also willing to help, just send me the stickers you want stuck, or make a trade.

how many can you send daily?

20 would be no problem, and right now, since I'm on a lot for morostide I could do lots more. It would give me something to do between ToTs and pumpkin patch. I could do 50-100 tomorrow.

i just made ten trades with stickers. just bid like 1 coin on each and i will accept so you can send them to me. i really appreciate it. go to my profile for the link to my trades