Some advice needed!

mdizzle but will give Turpes advice a trial run in London first
Good call. I don't really like to give advice on matters that come down so much to personal preference, like gear ratios, saddles, bars etc. etc. - I can only tell you what works for me.

Marseille itself is undergoing a serious regeneration right now, so you might be pleasantly surprised by how un-cesspool-esque it's becoming.