Let's hope it's still possible to join the HRE in EUIV. I remember a dev said in a post a long time ago that (I think it was Johan?) that he wanted more restrictions on that part.
They did add the restrictions in the last few versions of Eu3. You cant move your capital in and out of the Empire, and you cant add provinces if the Emperor sees you as a threat.
HOWEVER you can still get voted in as Emperor without being in the Empire. This is challenging, as there are opinion modifiers against external powers in the Electoral vote. In EU3, the easy workaround was to vassalize the Electors. That's obviously vastly harder to do in EU4 with vassal upkeep and the fact other electors will hate your guts for having one of them under your boot. But I reckon it will still be doable for a determined player. Of course, once you pass Renovatio Imperii, you get the HRE tag and can turn the page for good on electoral issues.
How is England #1 at diplomacy in 1444?
Surely Venice has a larger navy, equal or greater tech and more merchant power? Not sure about allies or vassals, but in EU3 England wouldn't have had any vassals at that date.
I'll take a stab at it. Big Ship Navy vs Galley navy. I bet the former counts for alot of points, and England starts with alot of them (40-50 IIRC?) whereas the Venetians are stuck with a Galley-based navy that may contribute little, and perhaps not at all, to the score calculations.