I've been meaning to try a vassal-spam Austria WC, so tips from your runs would be appreciated. But how on earth are you vassalizing the giant nations (is diplo remotely possible with the tax-base modifier?), and how did you manage quick HRE reforms now that electorate revocation has an AE cost?
Hauptman's Guide to the HRE;
Very first day I DoWed Trier with the revoke CB. Marched my army over and vassalized him... Second month, I DoWed Cologne for the same reason... Other diplomat was signing alliances with brandenburg and saxony, then improving relations... This gave me 2 Vassalized electors, and 2 friendly. Thus securing the next election.
Once the AE faded from that, I did it again for Palitanate giving me 5 votes, until Brandenburg started self voting. I was purposefully helping him grow. Then I fabricated a war with saxony through one of his allies and vassalized him.
When all hell breaks loose because everyone finishes their claims, there will be a lot of annexing going on... DoW when you get the liberation CB and release nations... That will nickel and dime your way up. It's slow and requires much war... but it keeps it moving.
Once the reformation finishes it's wildfire spread and you have the religious CB, it's time to start annexing electors. Target the ones with wrong religion neighbors. Annex, getting a CB on it's neighbors, hand out new electorate to a OPM you can diplo vassalize. The combination of handing out new electorates, forcing religion (through war) and releasing previosly annexed electors will finish you up quick. Until Landfriede.
Once Landfriede hits, all you have left is diplo annexing electors, and Aiding Imperial states in defensive wars. If you make nice with everyone with your now 6 diplomats, you can enforce peace in wars that include non HRE states, The game sees those as "defense of the empire". I didnt get a whole lotta chances to do that, I think maybe once, but every bit helps... Mainly a war with france got me through Landfiede. Once I passed the next reform (can never remeber it's name) and you inherit the throne... You can start canceling marriages and diplo vassalizing the monarchists within the HRE.
I was also aided by inheriting Bugundy, then rereleasing as a vassal. This gave me a nice chance to DoW france, and request Burgundian land back. After that I annexed Burgundy, added provinces to the empire, then released again. In total Burgundy gave me about 60 IA in the early game.
As far as the vassalizing majors. That's Austria's trick. You need to collect diplomatic reputation. Diplomatic and Expansion idea sets both give 3, Austria gets another 5 from an NI, and 20% of the worlds ivory will give you another 2. With full throne strength (uhhg brain fade, what's it called?) you get another 2.5. The half doesnt round up but it can help ofset a little over extension. In total you can collect 21 diprep with an advisor. There is also the rare diplo event that can give you 5 more for 5 years.
As long as you NEVER decline a call to arms you will build trust. Trust is key. it's worth 40 points in the vassalize equation.
Diprep 21
trust 40
military 20
threatened/friendly 10
For a total of 91.
Tax base caps at 90.
Also before you can get to the ivory, there are plenty of low tax base nations to vassalize with less than 91 points. Hungary, Poland, Lithuania even though large, are poor as dirt. Vassalizing them, adding provinces to the empire, then re releasing is HUGE IA. Hungary was early enough to help me get to where I wanted to be.
One thing you must avoid, is Revoke the privilage. It takes away 3 diprep. So it's better to just individually diplo vassalize the HRE states.
