I am currently working for all of the above options...look if you have guts to do something then no one can stop you..best luck
According to me join the company and learn more SEO tactics on different kind of sites and issuses. After getting enough experience you can try your own business or site. This will be more beneficial for you and client also.
Personally option 2 sounds good if you know a decent amount about SEO, you could do seo articles and site optimisations etc.
Yes. Actually dear at this time, my business is so small because I started it just 10 months ago. But I am in the seo field since 2002 when I was just in 8th class. When I feel that my business is so broad and feel difficulty to manage both then on that time I will leave the job and will give full time to my business.