Playing with France, the key seems to be more or less the same as with GB or UP: Colonialism. That is the answer. With it you get such an economic infrastructure that conquering Europe is super trivial. The main difference regarding GB and UP is that you have to pay more attention to the continent, especially in the beginning when Savoy (and some other minor nation) starts to annoy you.
No need to hurry in completing the Lousiana Mission. This is the last goal of this initial part of the game.First, destroy pirate bases and try to occupy as many trade slots as you can (if you temporarily block them with sloops while waiting for the merchant boat is up to your "house rules").
Killing off the pirates has the following benefits:
a) They stop annoying you on the trade theatres and trade routes
b) You get a couple more plantations
c) You get more colonies in America that you can use to recruit armies to conquer the mainland.

At this point, you should take your time to raise a decent army while developing your industries and colonies and researching bayonets (crucial!!)

Now you can address the mission. After succeeding at it, you will have great economic power. Taking advantage of having the additional recruitment bases, I like starting by the cherokee. I like it because I rather not leave my New France colonies unprotected. Once Cherokee have met their demise, Iroquois are next.
Meanwhile you should try to avoid war with GB or UP, because the possible pitfall of this plan is if they raid your trade routes. Having said that, you should naturally build up your navy not to run that risk.

The indian lands, plus lousiana plus the caribean colonies give a nice boost to your economy. Once you have a high income and a good navy, money will be flowing and its up to you to choose what to do. If you do go to war with UP or GB (which is highly likely) try to be the one taking the initiative so you don't get caught off guard. In any case, when war starts, the priority should be to take out their navy immediately so that they can't compromise your income.