From the ASSIST report, the missing courses you could have for CSUN and their units are:
1 ME 101
1 ME 101L
1 ME 186
1 ME 186L
1 ME 209
2 ME 286
1 ME 227L
Total of 8 semester units, since CSUN is on the semester system. These would be the “catch up” courses that you need to take at CSUN after transfer if you transfer there having completed all other courses listed in the ASSIST report.
You can take as many units as your want at CCs without issue. You will receive transfer credit for up to 70 semester units (105 quarter units) toward the 120 semester units (180 quarter units) needed to graduate, but all courses taken count for subject credit. See http://www.csumentor.edu/faq/transfer.asp#19 . So if you complete all available courses for your major, and all courses needed for either IGETC or CSU-GE before transfer, your transfer units may be capped at 70, but you will still be counted as having fulfilled all course requirements covered by your courses, including the “excess” courses over 70 units.
To determine how much space for non-technical electives you have after transfer, you can check the course plans.
For example, CSUN ME is listed at http://www.ecs.csun.edu/me/degreereqs.html . In junior and senior years, you would need 8 units of “catch up” courses (listed above), 40 units of required upper division courses, and 12 units of engineering electives, for a total of 60 units. This leaves no room for other courses unless you take overloads (more than 15 units per semester).
For CPP, the curriculum is shown at http://www.cpp.edu/~engineering/current/currsheets/me-13-14.pdf . it looks like there are 20 quarter units of GE courses shown in junior and senior years, but you would need 25 quarter units of “catch up” courses. So if you have CSU-GE or IGETC done before transfer, you would still need to overload by 5 units compared to the schedule (which already includes overload quarters up to 19 units) to graduate in 6 quarters. This would not leave room for other courses. If you do take an extra quarter or two, you could have space for other electives.