I will add questions and answers here as they come to my attention.

Why can't I find a team?

The obvious answer to this question is that there are not enough players in the search pool who meet your requirements and whose requirements you meet. What you can do to increase your chances is change your search requirements a bit. After you start searching you will see on your edit profile page a button "Search statistics". This option allows you to see how many players in the search pool meet your requirements, also there you can experiment with changing your search requirements and see how that changes the number of players meeting your requirements. The more players showing, better the chances are for you to find a team. When you are happy with your new search requirements, you need to stop searching, go to your profile page, change your search requirements there, and then press "Search" again. Of course the only real solution to this problem is larger number of players searching, which hopefully will also happen soon.

Is signing in through steam safe?

Yes :). Actually Steam OpenID login is more secure than standard login because your password is not saved anywhere on the server(only Valve has it). With OpenID logins you only need to be careful that you are forwarded to the right web page(i.e., check the address), for steam openid the website has to start with :"https://steamcommunity.com". As is the case with this website.