Sorry for the almost 1 year late response. Since then I have started another WC attempt with a ridiculously overpowered Burgundy, involving an early PU with France, and looking forward a late HRE unification (just to try something else than simply destroying it, and thus maybe achieve the WC much earlier than my 2 previous ones with France and Bohemia). I suspended it around 1630 though, in the middle of a rather dull series of Holy Wars with careful BB management ; then I got busy elsewehere for a while. I plan to to get back to that game and finish it (and I'll certainly pay more attention to building Trade 6 stuff then).I've done a pretty similar WC game as Austria, just using the PUs the Austrian missions set up. I thought it looked on from your first post. I suspect any Western OPM can WC via pressed RM claims, but my normal rule house rule on PUs is to disallow pressing claims via RM. Spies have enough disadvantages that I allow them but rarely use them. My Ottoman WC is the only one where I made extensive use of them.
I regard 1760 as quite late for GOV 53. If you had built enough trade buildings, you would have at least doubled your trade income. Its effectively quadratic in TE so taking 145 to 200 is a doubling, plus it makes it easier to kick everyone else out of your CoTs and get closer to 95% rather than 30% from your monopolies. Trade 6 buildings are very profitable to spam to the point of 200 TE in a large empire. Using that cash to get GOV53 20 years earlier cuts at least 5 years off the time to finish a BB limited WC.
About home rules, I must admit I might be pretty lax and allow myself a lot of shenanigans, including forced PUs, or spies that can do wonders when wars and diplomacy come at too high a cost or their outcome would be too random. As long as I have fun... and get things done.
For the moment I'll have another game that I'd like to post here... so please, let's keep this thread alive !