Class should be visible somehow, even if only by a sign near the character, for example a shield depicted on the left top of a character that is a knight, an axe for an axeman.
Most classes are really flexible, and none are as restrictive as an "axeman." I'd need a more complex symbol than that, but I symbol I can do. For instance, the "warrior" class is largely based on the Mandalorians of Star Wars (the only thing in that festering dung heap of a franchise I feel is worth my attention) so a tusked skull could be their symbol.
You asked how big of a demographic you would have, and it depends;
you 've not realy explained what the game is about except that it is based off a tabletop RPG ruleset, and i think that is your main demographic, namely table-top players.
Possibly, yes. And it's worth noting that it's not just "a" tabletop RPG ruleset, it's MY tabletop RPG ruleset. Which I made personally, by myself, with no help on the system itself and only very little help on the content. I feel that's important.
I think you should check out in that community a bit to see whether people would enjoy it, whether there s competition.
Way ahead of you: http://rpgforumsonline.com/forum/viewtopic.php?t=41739
If you still want to know about demographic outside table-top players, i suggest you rewrite your introduction and pretend that your listeners have never even heard about table-top games.
What about other fans of this small, vanishing genre? There are other games like this and some were quite popular. Fallout, for instance.