Portugal can be useful if they don't stupidly attack a 20 stack of enemy troops with 11k troops. Their best use is if France and allies attack them and you are nearby to reinforce. Portugal typically has anywhere from 10-20k troops involved in French soil so they are great to offset the allies France pulls into the war. The new income for England honestly makes it a lot easier compared to 1.7 where I was crying for every loss and having to replace them with more mercs I couldn't afford. You can actually match French + vassal numbers so long as you wipe one or both of the initial 4-5 stacks near Bearn. However it should be noted that the vast majority of the time you no longer have access to mountain terrain in Bearn(It's now hills 80%? of the time). Honestly a lot of the difficulty in the current version depends on who France allies and drags into the war. So far I've beaten France twice in the last two days, once in normal to test how hard it was and once in ironman. The first time they allied Hungary and some minor in the HRE and I never even saw Hungarian troops involved in the war. Needless to say that run was a joke. 2nd time they allied Venice and Savoy. All I can say about that one was that it involved a lot of hitting isolated stacks and basically creating rolling retreats by the French where one army would get broken and flee across the theatre of war and then consolidating, getting one tick of morale recovery and hitting a different stack until I managed to stack wipe one of them. Thankfully for some reason Venice didn't seem inclined to send anymore troops after the initial 10-15k they sent. Overall I think it's easier, when I did it in 1.7 it generally took 6 or 7 attempts to win, now I can generally do it in 2 or less. Lastly, the initial advisors are important. You want to restart till you have access to +5% discipline, +2 diplomatic reputation, and -3 revolt risk. Other than that the only other thing you might want is to make sure of is that Austria hasn't rivaled you so you can ally them after you win the war. They're extremely helpful if Burgundy gets it into it's head to declare war on you immediately after you win the HYW like they did in my first game. I barely had 3 months from the end of HYW before they attacked.
Edit: Forgot one thing because it seems so standard from previous strategies. In order to keep the PU with France you want to make sure to give France its cores from Provence. The bonus relations actually starts you at positive relations after the war.