I see that most of the people in France don't work the same way as most of the countries do (prints releases chapter by chapter), so here's a little background :
I've printed the first book of Echo one year ago. I did it via crowdfunding (the advantage : preorder there = more extras and bonus for the reader, like prints, badges, 50x70cm posters and more things I crafted for the crowdfunfing). The first book is a A4 size, 90 pages, black and white and colors + bonus. It contains the prologue + 3 chapters, got 80 copies of it thanks to a very successful crowdfunding (and 50 copies were for the project). So it is quite a big thing. I sell it 10€ because it worths it. When I buy a comic on conventions, it's mostly like this : dense (100 pages) to very dense (moooaaar pages), A4 or A5 size.
When printing it, we usually print 30 to 50 copies of it. 80/more copies are for comics that are some kind of popular, even if I think it's not that big! We use a printer on web, who makes good quality prints most of time (because somtimes, your book can turn bad and it's not their fault, it's yours. Bad guys.) and a good price. I know some printers around here, but their prices are too big for me... BUT they have a super extra quality.
You have to find a printer that is in your price range, and can make a good quality too. I think you can find on the forums some topics about printers.
If you want to generate interest on conventions, just make it attractive. Put it on good spot, with even one book example opened with a little bubble/character/whatever saying "read me!", so people won't ask you the permission if they can read it.
Talk about it with the people who seem interested. Like "Hello! I see you seem to enjoy it, wanna hear me about it?" but don't jump on them when they just looked at your booth. Be polite, nice, and everything's going good.
Also, +1 for Anna : stand up. Sketching is nice, but not everyone know what you're doing. unless you're signing something or you are tired, well.. Stand up ! XD
Last year, I offered a print of Echo on a textured paper to people who were buying the comic. It was a nice gesture, readers enjoyed it.
For selling online, I'm so bad about it I can't say anything. I was thinking about using Gumroad or Lulu one day if I translated all the first book, then just tell people "hey, like this? Well you can buy it, with EXTRAS in there. Yeah.".
And if it's works, yay! if it doesn't, well, too bad. At least the story continues, heh!