For digital,
Comixology is the way to go. I don't know about the rates, but they definitely have the audience and potential market for you.
For print copies, if you want to make a serious go of it, you're going to need to find a printer, and pay for a four color run (not just a digital scan, the quality is noticeable). This will not be cheap. Make sure you find a printer that you can work with and definitely get a sample of your book before the full run. This is also where you could consider a Kickstarter campaign to cover your printing costs. This is a whole other ball of wax, but I have 3 pieces of advice from my perspective as a retailer,
- Make sure your goal can cover more than just the physical rewards. Have digital rewards so that you're not having people pre-order. don't place physical rewards at the cost.
- Have a retailer reward tier. I can tell you that the odds of having my store back a comic project go down greatly if there's nothing I can sell at the end of it. Have a tier with multiple copies offered at a discount.
- Reach out to local comic shops to let them know about your Kickstarter. Point out the retailer rewards tier, offer to do signings when the book comes out.
Either way you go, but especially with print you should be hitting the convention circuit, which it sounds like you started doing already.
After you have your printed books, start going around to your local comic stores and talk to the owners about carrying your book. Give them a comp copy. If they're unsure offer up a consignment deal, this drastically lowers the risk to them. To jump back a bit, while you're looking around for printers consider
submitting your book to Diamond. Getting in Diamond means that every comic store in North America will see and have the option of ordering your comic.
Sorry if this is a bit rambling, but if your have any other questions just ask.