(Yes, I'm still lurking even though I'm not running this year).
PG3 - the thing to remember is that your race is at the end of May. I found myself getting freaked out by friends who were training for spring marathons, and my own expectations of the mileage I'd 'normally' be doing at this time of year. When people around you are pulling 20 milers plus at the weekend it's easy to feel you're getting left behind. But if you were training for Paris you'd have less than two months to go, whereas you have nearly four. It's a long haul.
Justin - welcome to the thread. Don't worry, all is not lost, you've still got time to get some miles in your legs. You've got 7 weekends between now and race day. I'd suggest focusing on the long runs, don't worry about speed at this stage. You could do something like 12 miles,14,16,10 (cutback week), 18,20,12. What's important is time on your feet, so consider doing these as walk/runs - by which I don't mean running as far as you can and walking the rest, but building in planned walking breaks from the start. For example, run 9 minutes and walk for 1. You're going to be on your feet for a long time on the day, so it's all about building stamina.
What TD said - we have a number of flags with a three legged stool on them (sorry, can't post pics from phone but perhaps someone else can?). They are in different colours - the Scottish massive have a blue and white one, the Welsh one is red, green and white, the NZ one black and white. They're highly distinctive and visible from a distance, so they make the supporters easy to spot. Especially on the end of a 5 metre pole (yes, I will be travelling to Paris with a 5 metre pole. It's collapsible ).
Ali 38 - I'm the same, after a long run I often find I can't face food for a while, but you should try to get some protein and carbs in within an hour of finishing. You can buy fancy recovery drinks, but ordinary chocolate milk (or chocolate soya milk if you don't do dairy) is just as good.
TOL - sorry to hear you're not running, but you and Mrs TOL would be very welcome to join the support army on the day - just come to the Arc at the start and look out for the flags. I really recommend getting involved as a supporter, it's very rewarding, although I should warn you that you might end up on your feet for longer than if you were actually running it .
Re the med certs - it's not just the organisers being awkward, it's a French legal thing, so the wording has to be exactly right. Participating in any organised sport requires a cert with the same wording, just the name of the sport changed, so it's the same for triathlon, cross country skiing, and, I'm reliably informed, Baby Gym (!). French doctors are used to supplying them every year but they do sometimes freak out non- French docs. For £156 I'd want a very thorough checkup indeed. Do bear in mind it doesn't have to be a GP who signs it - if you know any friendly doc with a stamp they may be able to oblige.