Not by itself. However, Manga+Press doesn't output markup other than the comic navigation. Responsiveness depends on the theme that is being used. The themes bundled with Manga+Press — the TwentyEleven thru TwentyFifteen child-themes — all have some level of responsiveness that is dependent on their parent themes.
Yes, it is! Manga+Press is simply a stripped down custom post-type with a custom Featured Image meta-box. Like any other post-type, you can add a new field group using ACF — however, you will have to configure your theme to display these custom fields.
I have never had the chance to test Manga+Press with the WPML plugin so I cannot guarantee compatibility.
Unfortunately, setting the Latest Comic page (or the Comic Archive page) to be your Home/Posts page overrides the queries that are run on that page to pull the most recent comic and the past comics. This is by design. I hope to add some functionality in the near-future to correct this.
I do take feature requests — however, there are a few criteria on which I judge each request:
Does the new feature fit with Manga+Press' current goals?
How well will the new feature fit with Manga+Press' current functionality?
The level of effort needed to integrate the new feature into the Manga+Press core.
The only themes that I provide support for are the themes that come with Manga+Press, which are child-themes of the default WordPress themes.