Hi Turnips,
As you will have read in the wiki, it is legal for two consenting, over 18 year olds, to exchange money for sex. So no need to avoid any "evidence" on your message.
I'm quite new to this myself, but on two occasions I have send a long polite message requesting my wants (clothing and activities) for a first meeting, and received a fairly short "yes" or "no problem" reply.
But both times, when I got there, they weren't dressed as I had asked, and I had the impression that they had forgotten my other requests - asking me what I would like to do. But once we discussed, they were happy to oblige.
I put this down to the fact that they get loads of messages everyday and don't have time to respond fully, or remember all of them (and some enquirys might be time wasters, so not worth the effort of remembering them all).
What I did find was that on the second booking (only a week later with each) they were dressed as I requested when I arrived, and remembered my interests.
So my advice is, yes, put it all in a message (as short a message as possible) but this is only to check that they will be okay with your requests. You will probably have to discuss/remind them when you get there.
Also keep in mind that English may not be their first language, and they may find it hard work reading a long message. - Another good reason to keep it short.
Enjoy your first booking!