So I just finished my run last night and figured I'd come give my thoughts on completion.
I didn't take any screenshots till the end, but here's what I ended up with at 1728 (completion time):
Overall there was really no rush to complete this, were I to do it over again I think I could shave a lot of time off by doing a few things differently. The hardest part was the opening and then dealing with muscowy, once that was done it was all very reasonable. I wasn't able to start colonizing till 1490ish (kinda slow) due to a long living, really bad diplo monarch and simultaneously eating up a lot of diplo points in peace deals. The trick people are doing with seizing colonies in africa to jump into south america early is brilliant, and definitely would have helped (as SA was where I had to have the biggest colonial fight)...that said, I don't know if I could have afforded to fight russia and fund colonies during the 1460-1490 period anyway as it was very touch and go, and I definitely think dismantling Russia early is of great benefit (or at the least cutting them off from siberia)
Even starting in 1490 I was able to to lock down virtually all of NA (france and england got maybe 10 provinces combined, but they were very easy to feed to my colonial nations). I did have a bigger fight in south america as france/portugal/castille/england did make headways there -- but again, its so easy to consume colonial nations due to the low warscore cost for colonies that it wasn't really much of an issue. I think at the worst point I had to commit like ~30,000 troops to south america to support my CN's. I basically prioritized forming CN's then moving on to a new region and only came back to try and lock up coastline, with the idea being once the CN was formed I could feed them rival colonies and natives and let them do the coring. This only backfired on me once in the la plata region when another CN annexed my CN outright in a war I didn't even know was happening. The problem here was the CN's were weak at first and couldn't fight rebels, so I would leave them 10-15k troops "attached" to their army until their OE went away. I guess the bottom line is despite missing a lot of south america it never really mattered, although I think my life would have been easier overall if I had made a stronger brazil.
The other thing I would do differently is work on becoming HRE much sooner. Literally it would have been my next major goal after taking down russia -- once I was HRE (and I had a lot of chances to vassalize electors I passed on) things got pretty easy. I didn't even start trying till around ~1650, although part of it was because I had a queen live like 65 years(!) making me ineligible, but I should have vassalized the electors in preparation for her succession.
Finally, I had a really big france -> they got an early PU with portugal, they both colonized like crazy, and then they inherited, which made south america about 50/50% split between me and france. France also PU'ed a naples that was 2/3rds of italy and hungary, and also managed to take roughly ~30 HRE provinces before I was able to push them back. They kicked my butt bad a few times, which was good honestly as once I was able to turn the tide on france the game got really boring
But had that PU not happened preventing me from DOWing portugal and eating their colonies without fighting france, I think south america would have been a total non issue.
On ideas: I went Exploration->expansion->offensive->innovative->defensive. I don't think naval is needed at all. Norways ideas cover it pretty well (morale, forcelimits, combat power for light ships). Plus your colonies give a ton of naval forcelimits. Exploration -> Expansion was a no brainer as maximizing colonists asap was key. I think for expansion I basically just grabbed the colonist and then left it untouched for a long time. I could debate offensive vs defensive for the third idea, but definitely military as I was constantly starved for admin points for coring and pushing for the next idea group -- and unlocking the norway NI colonist with unused military points was really the primary goal. Innovative was really about the tradition decay and war exhaustion modifier -- probably could have been replaced with something else and DOTF, but I had no regrets! I took defensive because despite full offensive and 100 tradition generals and baiting france into -3 mountains with equal or superior #s and DOTF (and +10% discipline for govt and equal tech) I was still losing about 50% of the battles and taking larger losses, lol. Once I had the morale bonus and was able to tank their prestige that issue seemed to stop.
I really liked this one -- it's definitely one of the better "difficult" achievements as there's a lot less monotony vs like a world conquest or jihad, etc!