Wanted to make some silly plans with an OPM that was absolutely not settled for them :
I chose Modena because, whereas their PU senior partner Ferrara can get into some trouble (The Papal State has a specific mission against them for instance), everybody around seems to ignore completely that pale yellow OPM. AI Milan doesn't even consider asking them for Military Access, which is a shame since this is how they consistently tend to fail at fighting rebels in Sienna and Pisa and so often end losing those 2 precious provinces. Of course I didn't bother proposing them either, so I could vassalize the new independent Pisa state later on.
I just had to refuse the alliance with Ferrara and let them die alone. Very soon they got seized by a pretender, which broke the PU and I was set free with a new and rather decent ruler, without having even asked for it. Then Ferrara DoWed me to restore the PU, they lost and became my loyal vassals. Oh, how the tables have turned.
Another reason for choosing Modena over Ferrara was that I intended to sail West - here the silly plans begin - and at least Modena is on the right side of the Italian Peninsula for that.
So, I took advantage of my University to get National Ideas faster, and being an OPM (and HRE member) allowed me to swap ideas whenever I needed it with stability hits not causing trouble for too long. I could choose QFTNW during the 1420's and colonized Madeira. I couldn't colonize very fast though, because even with Trade tech 7 I was not a very good trader, and in spite of Modena being a decent wine-producing province, I was constantly broke due to the expensive things I was doing overseas. Besides, something completely unexpected happened in the middle of the process : a PU with Castille. This allowed me to win that defensive war against Venice you can see on the picture above. The downside was that Castille involved me in European stuff more often that I'd need (Aragon was willing to reclaim that Valencia province Castille had taken earlier).
Actually my purpose was completely elsewhere :
I was finally not going West, but East. Modena decided not to trust the wild imagining of that Genoan navigator, Cristoforo Colombo : the road to India had to sail around Africa, period. I paved my way by conquering pagan countries instead of colonizing, it took a while but was also much less expensive. I finally conquered all of Mutapa and waited a bit until everything was cored and converted... then went for India with a foolhardy 20k army (who eventually won against Vijaynagar but was rather badly decimated, I have to admit. Galloglaigh Infantry is not enough against Indian troops apparently).
Fast forward some dull decades of conquest. During the 1530's my excellent, 85 year-old king Francesco died after a 70 year-long reign (!) and I inherited Castille. His heir was already 73 years old (some Prince Charles vibe here) but still lived long enough to be elected emperor. As you can imagine I couldn't care less about HRE stuff, but the news was welcome for the manpower boost (I still had issues with it back then).
I also had directly inherited Mantua earlier on, without even having a PU with them. Thank you, but that kind of ruins my plan of keeping my capital isolated until I'm ready to leave...
I wasn't really happy with that Castillan territory since it gave me Overexpansion (my Indian possessions were far from being cored). And I needed Castille alive as an ally in Europe, not only for their armies but for the big fleet they tend to build. So I released them as a vassal. In the 1550's, when Nova Modena (former Ahmadabad) and surrounding provinces (including Kutch and its juicy CoT) got cored, I also released Mantua, adopted a Republican government, rightfully lost the Imperial Crown, left the HRE... and moved to India.
It was said that I would still get some trouble from Castille though. Here I have just been DoWed by England for a stupid colonial dispute with Castille in North America... Don't you think I have some more important things to do, kids ? Like attacking former OPM Delhi who just made a spectacular comeback... and that unusually big Assam, too.
I was kinda exhausted by the game at this point, so I stopped there for a moment, but I guess many funny things could still happen. It was never as easy as it could seem though, because Modena is not Holland and the route I took with them was not obvious, really. But it was an original experience.
(Final sidenote : Switzerland went berserk in that game, probably got the "Claims on our rivals" event several times or something : whatever, they completely destroyed Austria, and for once I took zero part in it. Impressive.)
Edit : forgot to mention the incredible resistance of the Hordes in that game. Golden Horde falling to Muscovy and Prussia is quite recent here, in the early 16th century they still held Crimea, since Poland and Lithuania completeley failed to conquer them. The Timourids were struggling but after my first war against Vijaynagar they took advantage, took back some of their coastal provinces, vassalized the minors that had rebelled away from them, and even contained the expansion of Persia for a while. Other Hordes were mostly intact, and thus still in TI from the Westerner's point of view.