I work in newborn ICU so will give you a few suggestions from my nurse brain.
Remember it will be hotter in SO Cal than you are used to at home so please remember to take in extra hydration for your milk supply, and try to nurse him a little more frequently even if he doesn't ask. He may not know he needs more fluid. If you are bottle feeding still remember to take in more fluid for yourself and give him a bottle a little more frequently. Your other kids may need to be reminded to drink more frequently also.
Also many of the sunscreens out there are really not baby friendly so check with your pediatrician before you go to see what they recommend for suncreen so that little one does not get to much bad stuff absorbed into his skin.
When he is in the car seat on the stroller please keep it fastened just like he is in the car, the straps should be snug with no slack. Many people do not realize how close they get to strollers with car seats and if he gets bumped or heaven forbid tipped over having the straps secured will keep him from injury.
He will get hot in the car seat so taking him out after about 2 hours, even if he is sleeping, will help him to not overheat. I like that you plan on wearing him some of the time, it will be great for both of you.
Now for you, remember you are still healing so don't push yourself to hard, take some extra breaks and a nap if you get a chance. You know your body best but some rides that would normally be okay at another time may not be okay now. It is ok to not go on every single ride.
Since grandma is in a scooter if you take it at her pace (not the whirlwind children's pace) that will be perfect for everyone involved. Well the kids may think different as they want to go go go, but I think you know what I mean.
Now stepping out of my nurse role HAVE FUN.
Also take advantage of the photopass photographers and don't forget to take the little guy out of the stroller or the snugly to get him in the picture.
