First find out if the paralegal certificate will even get you a job. That means calling around and talking to people that hire paralegals, such as legal temp or legal placement agencies, law firms, etc. Act like you're doing an informational interview, set an appointment if necessary. It may be that the paralegal cert. won't cut it, or that there are no paralegal positions available in your area b/c of the economy.
Also, you need to figure out what your work schedule will be like assuming you can find a job. Will that work with the classes you need to attend to get your BA? Can you do the BA part-time and work full time, etc?
Lastly, I would not get a BA in poli sci. You don't need that to go to law school and it won't help you once you are in law school. Get a degree that will actually help you find a job or do something else in case law school doesn't work out or if you decide to work for a few years before going to law school. In other words, do not get a liberal arts degree b/c they essentially have no value on the job market.