Manga+Press leverages WordPress' functionality as much as possible for seamless integration with themes. However, issues can still come up. Download and install the plugin. Test against freely available 3rd party themes, or popular free plugins. I presently do not support premium themes or plugins.
If you find a bug and have a fix, please fork the repo on Github and create a pull request describing the bug you found. I'll review and determine if the fix is safe to merge, or make suggestions on improving it. And yes, you will get props in the next release.
Finally, the biggest area that help is needed in is multi-language support. Currently, Manga+Press has a Spanish-language version but I am not a native Spanish speaker, and I'm relying on Google Translate for my own translation needs.