Well there does not seem to be any h titles worthy of seo worked in atm.
You would be relying on mainly page title as there is little textual content.
For example the "architecture and artistic consultancy" title would be an excellent h1 source title if in text which was indexable and anchored, you will only get an alt tag in there if using an image for that which wont carry as much weighting compared to a h1, h2.
I would up the body font size to 0.8em as a minimum.
Possibly make the prev/next buttons higher contrast (end button bits are nice).
Possibly up the h tag font sizes if they look too small compared to body size.
Input fields on contact form look too wishy washy, would stick in a darker border to make them more defined, possibly change colour to their green rather than pink.