I wouldn't post my email address unless it's to someone I know I want to continue to communicate with. Then, I would put it in a private message.
Keep in mind that with a private tree that is searchable, people will have to contact you to get more information. When they contact you, you don't have to give them access to your tree. You can just answer their questions.
I have asked a lot of questions of people who have private trees and none of them has given me access to their tree -- and I haven't asked for that. Most of them have answered my questions which has been sufficient for me. However, some don't even answer at all -- which is an option for you if you don't want to communicate with this person who took all of your research. I also believe you can "block" another person from contacting you. I see that option when I click on the tree-owner's name at the top of any page on their tree.
Also, I have never had any problems with the message service. I think recent failires must be a temporary thing -- perhaps because of all of the trouble Ancestry has been having keeping their system up and running while they make some hardware changes.
I hope this helps!