First off, good luck! Secondly, some links.
I'm finishing up a England/GB achievement run (35 years left). I wasn't as aggressive as I could've been, so it wasn't a WC, but is ending up fairly well. Shameless self-promotion,
check it out here.
Before my run,
I asked many of the same questions here.
For specifics on the HYW,
I found this thread invaluable.
One of my biggest regrets in the run was not taking Religious much sooner. Don't know where it would've fit, but the Deus Vult is rather powerful. Once I realized how powerful, I took it as 4th or 5th idea only for Deus Vult, and refunded the amount once Imperialism was available. Deus Vult is ridiculously good against ROTW (and heretics) not necessarily because it lets you war with a CB, but simply because all their land becomes justified demands, allowing you to take non-claimed land at 0 DIP, saving precious amounts for integrating vassals, tech levels (don't get too far behind or your ships will be behind & you'll be crippled colonially), idea groups, reducing war exhaustion (sure to be needed often), and other war options like returning cores or releasing nations.
On that note, one thing to remember is that if you go the vassal route (which, as a non-core-heavy nation is good), forcing return cores can be handy for getting a vassal's attitude high if you've recently annexed several. E.G., in my current game, I can't annex Nogai because of a -150-ish modifier from annexed vassals, whereas some other vassals got a +200 to relations because I had returned cores rather than simply transferring occupation & taking the land. It might cost a little DIP, but helps a lot.
I generally don't recommend choosing an ADM idea for a first one, since that slows down your 2nd idea group. DIP is almost always my first choice.
Finally, while winning the HYW can be painful, keeping France is I think more painful. She'll try to get independence all the time, and even if you keep her at +200 with Improve Relations, she gets frequent events for a negative malus. Beheaded Nobles, Backward Monarch, and another one I forget. In my run, I ended up on the third attempt to just take land. If you opt for the PU, a highly recommended option I've seen is to make quick war with someone to release Guyenne after the HYW. Because you have a core in Guyenne land, and France has much of it, she'll be forced to give up her Guyenne cores as well. Then you can conquer Guyenne and take the lands for yourself later. But this weakens France enough to help reduce her independence desires. I would integrate ASAP.
edit- p.s., I also regret not taking on colonies/colonizers sooner. While Castile & Portugal were essentially crippled on the main land, their NW colonies were a PITA and continued to grow. If you act fast, taking out their island holdings and taking Arguin on Africa's west coast help to cut down their range.
Also note that you can't core Iceland until you have at least one of the islands between Scotland & Iceland cored. Another reason to improve your DIP tech is to increase your coring range.
