You can provide any number of fandoms or characters you want for a prompt. If you do too many, your prompt will be harder to write and ay not get filled. Phrases or words are optional as long as you specify at least a fandom. Requests for any fandom any character are permitted, just be advised that if filled, it may be for a fandom you are not familiar with.
As to spoilers, that's correct: we're trying to allow for the international nature of the 'net and give folks a chance at (legally) seeing things from other countries without being spoiled for them.