I've done a few marathons before although not this one. My advice re family and freinds is not to have them try to follow you on the course, it's never worked for me. Possibly get them to wait at the half way point, a big cheer can help, and meet you at the end.
Something I did in my last one was to write my first name in BOLD somewhere on the front, I lost count the number of times I was cheered on by name by complete strangers, it helped through a few rough patches ( and there will be some!)
Most of all, don't get cought up in worrying about pace/time, as it's your first just enjoy it.
BTW with the help of my club I've just been accepted into next years London.