Welcome to the Apple community.
I certainly haven't had any issues with Lion, although I am aware a handful of third-party applications have yet to be updated for it.
You won't lose your email address by not updating to Lion, but you will lose it if you don't migrate your MobileMe account to iCloud.
Lion is available from the Mac App Store which you should find in your application folder.
By the way, I use a Mac pro too.
Snow Leopard is unable to use the majority of features included with iCloud, you can however use iCloud mail in the mail application if you enter the settings manually. You can also access your mail, contacts calendars and all the data in iCloud in Snow Leopard by using your web browser on the website iCloud.com.
I'm not entirely sure about the upgrade from Snow Leopard to Mountain Lion, but I rather think that you need to upgrade via Lion.
If you do decide that you wish to use your mail application for iCloud mail once you migrate from MobileMe to iCloud, you will need to delete your mail account from Mail preferences and set it up again using the Mail Server Information.