OP,
I’m also a CCC transfer applying to the UC’s. In my case, I will be looking to double major. Due to scheduling purposes over the 3 years after transfer, I will take summer courses in Summer 2018 right away in June. However, Summer 2019 and 2020 will be research/study abroad. So the summer courses will solely depend on your goals as a student.
My two cents: I’m not sure what you mean by increasing your chances with the summer courses. Your application will be reviewed and decisions out by April 30th. Anything after that date, I imagine would not be taken into consideration for admissions purposes, i.e. spring grades, summer grades/internship. Unless of course you desire to have internship/research work each summer for Grad school purposes. That I can see being relevant.