I'd probably just move straight to 10k, you'll have sufficient base fitness, and once you have that, the jump from 5k to 10k is a lot easier than the one from 0 to 5k.
A marathon is also more than do-able by the end of next year, particularly if you have a good base fitness from your job. I did a pretty hilly trail marathon back in June and spent a stretch running with a woman who'd only been running around 6 months! Not saying everyone could do that (i couldn't after 6 months), but it's possible, especially if you put the work in and are happy to follow a structured plan to get there.