You've said that you've got ComicPress loaded, but you'll also probably want:
-ComicEasel (gives you an upload system for adding pages easily - click "add comic" and then use "featured image" in the top right to pick the image, also gives you a navigation bar that you can customize or reskin and an organization system for chapters, characters, locations)
-Google Analytics (Lets you see your traffic, where your traffic's coming from, what pages people visited, etc.)
-Photo Gallery (Let's you add/organize galleries and then easily add them to your pages. There are other plugins that do this, but Photo Gallery seems the least limited in the free version)
-UpdraftPlus (helps you easily create backups and restore them in case something goes wrong, you get hacked, or you need to migrate your site)
-W3 Total Cache (optimizes your site so that pages load much faster and you use less resources - will be necessary to withstand high traffic - just remember to clear the cache after you make changes or they may not show up for other people)
Those are my personal choices, anyway. Other people may have other suggestions, and ultimately it's up to you.
Also, post your stuff on reddit. Even if some of your posts don't do as well as you hope or a few nasty people say something mean, be tough and keep posting. It's the best way to generate traffic for your site and accumulate returning visitors. If you don't post there already, there's /r/webcomics and /r/comics.
Hope this helps!