TAG actually IS a guarantee (it stands for Transfer Admission Guarantee) so long as you meet the requirements:
http://admission.universityofcalifornia.edu/counselors/files/tag-matrix.pdf
http://www.admissions.uci.edu/applicants/tag.html
Do you have any upper division units from your CSU? If so, be wary of unit caps.
Your ECs look excellent. There are 2 PS prompts, which can be found here: http://admission.universityofcalifornia.edu/how-to-apply/personal-statement/
Brainstorm some ideas, get some feedback from trusted friends/teachers and see what you end up with.
Edit: website to submit TAG https://uctap.universityofcalifornia.edu/students/index.cfm