Do you want to be French (the more conservative/classic Ines La Fressange vibe that only nods to fashion from very far, see also Justine Leconte) or Parisian, and if the latter you're going to have to be really specific ; A Quirky Creative from SoPi, Faux Creative Trend Obsessed (or more likely since its their natural habitat, a gay man) from the Marais, or the understated elegance of the Seventh, That 70s Sorbonne vibe, or the utterly cool yet strangely unkempt look of the 11th and 12th that's up and coming, or one of the many other Arrondissement styles? The whole Parisian/French thing is all about the details and very determined decisions, careful, much antagonised, choices and a highly oppressive standard of beauty they've been raised to adhere to from a very young age. They're the biggest market for anti-anxiety meds globally for a reason...
To add to your list:
Short well kept nails, never painted (a dark red maybe on a special occasion), clear varnish or a faint pink is ok but more for the manicured professional lot. Never a French manicure.
Be a secret Anglophile. All French style icons are foreign women, and a lot are from the UK, Jane Birkin, Charlotte Rampling, etc. If you look at a lot of brands they reinterpret British Heritage styles with a more slimmer and feminine fit. Soeur has a shit ton of 70s inspired British Heritage stuff in right now but in a totally French way. What we call French Girl hair they call Boucle Anglaise. So, be British but not really 
Sit down at a table for every meal and start with vegetable soup (no dairy). 3 meals a day and breakfast or a snack usually is yoghurt or fruit. I don't think there's a miraculous secret to their thin frames in terms of diet aside from being more discerning about the quality (though that varies too), they do have an irrational fear of being fat tied up in oppressive beauty standards so there is that but they naturally are small framed and petite, so even if carrying a bit of extra weight they still appear slim to Northern European eyes.
Spend more money on your scarf than on your coat or, buy a new scarf for coat money instead of replacing an older coat.
Very fine jewelry, and never noticeable or ostentatious.
Your style icon is not a celebrity or model but rather your Mum, or, preferably, a crazy aunt, godmother, or grandmother with an outrageous treasure trove of a wardrobe and even more outrageous stories to go with each an every item in it.
Have a signature scent. Preferably a very obscure one.
How to be Parisian by Caroline Maigret, et. al. is surprisingly good reading despite being a bit of a fluffy gift book by appearance. Violette_FR on youtube is good for makeup without being that heavily restrictive no makeup makeup look only (she's a Parisian in New York, ie. she's allowed more liberties). I'm obsessed with Les babioles de Zoé's hair which is neither laissez affaire or low maintenance and she's pretty representative of Parisian style but not necesarilly ticking all the repressive boxes but it is one most will not be able to copy directly one to one but use rather as inspiration.
