And yes, a factory reset will wipe all user data including email and texts. A complete backup would be prudent, but you should have backups already because phones fail and data is vulnerable.
If you have apps and settings set to backup (menu>settings>backup & restore) with auto restore on, as soon as you register with the gmail account, the apps will reinstall themselves along with their settings. App data, OTOH may not get restored ... things like game levels or usage history. Make sure it's set to sync the account to the cloud so you don't loose any pictures, contacts, etc. If these settings are off now, turn them on and give the phone 24 hours to sync completely before resetting.
For text messages, SMS backup & restore in the play store works great. Email will depend on how it's setup. If it's an IMAP account, then you're already good since everything is always on the server. IF it's a POP3 account then you'll need to copy the email you wish to keep off the phone.
And please always verify that the data you want to save is saved before resetting. I can't tell you how many times I have to tell someone sorry your data is gone because they "thought" it was working even they never checked.