I'm not in any way knowledgeable about Ha Noi since I've never been there but I put a lot of effort into trying to get to know VN in my first 6+ months here and I see lot's of possibilities for new businesses in Vietnam. I don't know what you are your guy's legal status will be while here but the visa status thing is a hurdle to jump here so I'm not saying that it's super easy to start a business in Vietnam but it's also not impossible.
On you English job thing [your guy as well if he can find a French teaching job], can I make a suggestion? Listen, if you have your certification, clearance letter, cv, and id ready. You can contact some schools and get interviewed / hired to teach English before you leave for Vietnam and your employer can get you setup with a contract, work permit / proper visa arrangement before you arrive....maybe. I read about it but did not do that so maybe I'm wrong but I think you will be at least 100% better off if you do that so that you can avoid the visa runs and hassles of no WP etc. I wish I had tried to do that in retrospect. Don't forget that lots of teachers are teaching illegally on tourist visas and it's not a problem until someone decides to make it a problem and then you may regret it. Everything is better in Vietnam if you are compliant immigration/wp-wise, banking, employment, etc.
Just some advice if it can be done it's much better than arriving as a tourist. I'm not an expert but it cost you almost nothing to do the research now and try to land a job before you arrive as you've got just enough time to get it done before a July arrival. Don't forget to tell you potential employer that you want a minimum one year contractr and work permit. They will tell you ..'Hey it's not necessary yaddi yaddi.' IMHO a quality school will be interested in getting you locked up in a contract for a year or more....the lesser schools are always trying to skirt the law often to the expense of the teachers and it's all because the VN don't want to pay a 4 million dong to get you legal. If a potential school won't give you nothing but pie in the sky promises until you arrive then you should put that school on the backup list and keep hitting up schools which are serious about have a professional relationship with you. Maybe you get lucky. Stick to your demands and keep contacting schools and tell them you will only work for them if you get a proper legal package.
But you do need to get started pursuing immediately as the package can't be thrown together in less than a month's time etc. etc.
Good luck.