Well there are lots of facets to photography, I personally do as little portraits as possible. I don't really like to photograph people! It's cool that you really enjoy it. If you decide it's going to be something that you do on the side, it's going to be difficult to do types of photography beyond portraits and weddings. Just because those 2 may allow you to keep a foot in one world and another foot in some other world of your choosing. Finding assignments with agencies typically requires a sizeable investment of equipment and years of experience building portfolio material and contacts / networking in the industry. So it would be rare for someone to do these types of projects and not be fully immersed in photography as a career choice. Good luck to you!
I really like working with people, but I wouldn't say that senior or family portraits are my favorite. Other types of less-conventional portrait photography are what I enjoy the most! For my own personal enjoyment I like to do fine art and landscape photography.
As far a working with a marketing company like that, I actually have already started doing that! I have connections with a small specialized marketing agency and occasionally I will work with them for one of their add programs or political add campaigns, and I really enjoy it. So through them I would be able to keep working with them occasionally and the owner, who is the one I know, is able to help me get connections. Through him I have covered events, such as debates, for different foundations and done things like that. And I really enjoyed that.