As for France, you play with Lucky Nations? I heard it's complete balls and people advised on not using it.
The term 'Lucky Nations' alone was enough reason for me to turn it off. You are playing a game where you can shape an alternate history, how is it fun to have the same half a dozen superpowers everytime?
As for playing England, abandon mainland Europe, unite Great Britain, build 50 Carracks and laugh at the silly French 80 army at the other side of the pond. Then colonize all of Murica and come back later with a 200k Europe invasion force. When I played England till about 1700 I never had more than a 10k army sitting in Britain, not a single enemy ever set foot on my lands after I united it. That was one of my first games and I had 70 ships covering 160 overseas provinces, don't do that. I just couldn't figure out why my tarrifs were so low
Trying to hold your mainland stuff is a fucking pain and not worth it in my opinion, but perhaps it is a nice challenge cause otherwise England is a walk in the park. For the battles thing, maybe it has to do with discipline, with yours being very low or something. I have never been entirely sure what it does.
You can fix overextension by pushing the decentralisation slider.
I find overextension not that bad to be honest, as soon as the nationalism fades out there will be hardly any rebellions, especially with some courthouses. Besides, I can spare a few thousand troops as civil police. Nationalism just lasts 30 years, hardly a much slower solution than pushing sliders back to craptown. I have only 20% cores anyway, so I think I will just have to live with overextension for at least 50 years. I thought I would get cores on all of the HRE members provinces, but turns out you only get cores on a few central German provinces. Yet with 80% non cores I already get 5k a year which is 5 times what Castille gets, the second economy, HRE is truly redonkeylous.
I think i spent over 500h on EU3 and never finished a single SP game, most of the time you can stomp everyone after like 200-300 years so thats when I usually stop and i'm too much of a pussy to play something like chimu, MP is where most of the fun is at imo.
In my experience playing multiplayer reduces the 'time until you can stomp everyone' by about 300%, which makes it more boring to me than the singleplayer. I have only played fully cooperatively though. Playing competitively wouldn't seem that much fun to me, because the guy who selects the more powerful starting nation wins.