Hello there,
I am a webdesigner and texte (so assume I have a fetish for readability) from Berlin. I have already done various templates for e-mails and could send you one as a working example. I normally test for hotmail, gmail, gmx and the interfaces of thunderbird and outlook as well as on an android phone, but if there are other common mailproviders in france, just let me know and I will test them, too. The real stumbling block is not the responsiveness, but what the mailproviders do to inline-css.
Your mentioned points for design are easy to adapt. Things I would like to mention:
1. Espacially on mobiles, pictures are often not loaded, so there has to be enough information without pictures to make the readers trigger the load of the pictures.
2. I would recommend to keep an at least abstracted version of the colourscheme for an initial recognizing, without the logo and just clearifying, who the sender is with text, as pictures wouldn't load from the beginning anyway and will never be, if the mail doesn't catch the attention in forehand. And the headarea shouldn't look like shit until the pictures are triggered.
There is just one thing I can't do for you: I don't work with Photoshop. I always develop in the browser for native responsiveness directly from the start (and too, it costs less time and therefore less money). If that is no dealbreaker for you, I'd be glad to hear from you and send you an example of my work.
Yours sincerly, Dorothee Schuster