It's looking good

Red on black or black on red can sometimes be a little hard to read. The text with the white borders stands out a lot better - perhaps it would be worth adding a think white keyline to some of the other text as well. For the block at the top you could also try doing it as white text against a red background.
lejimi wrote:About the fonts, I noticed that it's better to convert them to path before creating the pdf. Else, using the option when exporting, creates a pdf document with ugly fonts : way too much weight. Is it the same on other systems ?
That's been my experience as well. I always convert to paths myself rather than relying on the option in the PDF export dialogue.
lejimi wrote:I made differents tests. One way is to export in png, use Gimp to create a jpeg (no png accepted by the shop), then convert it with CMYKTool (I thonk you can find it on Ubuntu's repos). The other is to create en eps file (strangely, my Scribus can't deal with Inkscapes pdf), import it in scribus then save as a quadrichromic pdf. The last way is to delever an RVB pdf and ask the shop to convert it, but once again, it won't do with online-shop.
I tried various approaches with my print shop, and finally settled on a couple of options:
1) If there are no gradients, filters or other such things in the image, Inkscape's EPS or PDF export seems to work pretty well for them (though sometimes one works when the other doesn't, so I often export both and let them choose)
2) For anything more complex I export a high-res PNG, convert to another format if necessary, and accept that the best they can do is place it as a graphic in InDesign.
In my experience the RGB files I produce tend to come out very dark when printed. Simple lightening doesn't work for me, as some of the paler colours get lost. So I tend to lighten things a little in Inkscape, then adjust the colour curves a little more in The GIMP if I have to, and finally just accept that some of the colours will be "wrong" compared with what I see on screen. None of my equipment is calibrated and I don't use a CMS, so all I can do is iterate a bit, and hope for the best.
Bear in mind that Scribus can load SVG files directly. There are limits on what it will render, but simple flat colours and paths should be okay - perhaps you could just load your Inkscape file directly into Scribus and export a PDF from there.