It’s complicated.
Taking coursework at a CC is non-ideal but it’s not a total dealbreaker for med school.
While it’s true that some medical schools will not accept CC credits to fulfill med school admission requirements, many will
IF (and this is a very important IF)
you take additional upper level credits to supplement any CC science credits that you earn.
For example, if you take 3 quarters of intro bio at the CC, you MUST take at least 3 more quarters of upper level biology credits when you are at your 4 year transfer university. If you take 3 quarters of gen chem at the CC, then save ochem and biochem for the 4 year.
Now this may mean you will have to change your preferred major so that you can fit in all the required classes for graduation in your major AND take the rest of your pre-reqs.
I know that you need to earn enough credits to transfer to your desired major and that will require taking some pre-reqs at a CC–like intro bio and gen chem. But try hard not to take more sciences than just the first year of biology and chemistry. Then make sure you take ochem, biochem plus several more upper level bio classes when you get to your transfer college.
You can certainly take your GEs at a CC, plus non-science pre-reqs like writing skills, intro psych, intro sociology. You could even take Calc 1 and stats. ( If you do take the math classes at a CC make sure to take a biostats class after you transfer.)
If you go the CC–> UC route, you will not be able to apply to medical school until after you have graduated because med schools will want to see a final transcript w/ your UL elective grades from your 4 year college because there is a perception than CC grades are inflated and the material taught is less rigorous. Med school adcomms will want to see how well you fare against the tougher competition at a 4 year college.
You will also need time at a 4 year college to get to know your professors so they can write strong LORs for you. (Letters from CC instructors are consider “weak” and will hurt your chances for a med school admission.)
This means you will have to take at least 1 gap year before med school. This isn’t a big deal and >65% of incoming med students have taken 1-3 gap years before med school. Use your gap year wisely to strengthen your application.
As for whether you will need an extra quarter/year at your 4 year–that really depends on your major and how well you plan your class schedules.
I can’t say whether UCR or SLO is “better” for premed. As @Gumbymom points out they both offer everything you need. It’s up to you to find out about the resources the school offers and to take advantage of them. My older D did her first year at SLO and hated it because SLO turned out to be a very poor social fit for her. The academics at SLO were just fine.