Newbie planning trip California in Autumn

Hi
Coming from Europe and new to bikepacking and planning a 5-10 day trip to California starting in SanDiego in last week September 2018. I have made one solo bike trip several years before to Spain from Netherlands ~ 1000 miles. I have no experience with long trips on a MTB.

I am asking your advice on;

1- Wondering if it is still to hot for a multi-day tour in the San Diego /San Bernadino / Mohave
2- What is the best place to rent a bike. I have contacted Topanga creek, they are offering a Surly Ogre with 29” x 2.5 wheeled bike. Seems really nice bike/shop
3- Any advice on nice routes I found Bikepacking.com Stagecoach (5 day) and social-desert-ramble (10 days) . Not sure if they are too much...

Thank for your help !

Marc
Bike: Koga Miyata Globaltraveller