I encourage you in your creative pursuits. There are, in fact, web manga out there; we've had some submitted to Kumoricon's fanfic / manga /webcomic contests before.
Without knowing what plot or setting you have in mind for the characters, it is hard to give further feedback.
It's fun, though, if you design characters that would be entertaining to cosplay. First year of KC, 2003 in Eugene, in addition to Integra Hellsing, my other cosplay was Seraphim from Megatokyo.