1) Does email count as getting it in writing, or do I need an actual printed document?
Ideally a written document. But a document on company letterhead in .pdf format would probably be fine also.
2) Am I getting this from the affiliate places (tradal etc), or from the casino sites (888.com etc)? Or both?
Again, ideally both. But, in this case I would be satisfied with a written guarantee from Tradal as they are a reliable partner to work with if everything is clearly outlined and understood by both parties.