I am not sure either why you would need to use calibre for comic files. On an android device loaded with perfect viewer, any comic you download in .cbz or .cbr format will be fine. Also, if the comic is a .pdf, the add on in perfect viewer for pdf files works a treat.
I tend to download files to my pc, then drag and drop to my external sd card on my tablet. Keeping a few micro sd cards lets you have a huge range of comics, storypapers and other stuff to read, whatever takes your fancy. Although I don't think kindle has the option of adding a micro sd card, but I could be wrong.
What I would suggest is treating yourself to a big screen device. I use a Samsung 10.1 tablet and comics look really good on it.