Hi Peter,
1- It’s default image of JA Masthead module, you can go to Admin panel > Extensions > Modules > filter the JA Masthead module in ‘masthead’ position > add the contact page in menu item field and add your desired image in ‘Background’ field: http://prntscr.com/ijr4w9
2- I guess you’re mentioning the social in contact page, right? They are links set in the Contact settings: Admin Panel > Components > Contact > open the current contact > Display tab and you can change the social links: http://prntscr.com/ijr5bq
3- Make sure that when you enable the URL Rewriting option, you need to rename the htaccess.txt file to .htaccess file.
Regards