Would you recommend accepting the liberte, egalite, fraternite event, or not?
The penalties regarding unrest and missionaries don't appeal to me, but technology cost is lowered, and it might be interesting.
I did in EU3, but haven't had that event in EU4 yet. I suppose it depends on how advanced you are already. In EU3, you could always keep advancing in tech, even if the ahead-of-time-penalty became decades, since there was no limit on how much you can invest. In EU4, once the tech cost is more than your max monarch points, you've hit a wall. You can still invest them in more buildings, but only if you have the cash. Which may be the case late-game. So it would be situational for me, and less of a yes-please than in EU3.
IMO, the slow manpower regain is one of the most important changes in core gameplay in EU4 (and technically the last patch for EU3, 5.2). In EU3, you'd almost always have plenty of manpower even as a mid-sized country; in EU4 you often have to be careful even as a large country and manpower often (though not always) is a limiting factor in war. I was actually surprised in my most recent war that manpower was not even close to a limiting factor, but I had 350,000 to start with due to Quantity ideas and a large-scale armory-building programme.
EU4 in general, though, has a lot more nuance than EU3 or Civ. In EU3, once you got to a certain size, you pretty much could go do whatever you wanted as if it were Civ, provided you stayed under the infamy limit. EU4 does a lot better at making the grand strategy aspect last later in the game, but it does mean that you can't be at war all the time (although this does vary somewhat by patch; 1.6 in particular being war-friendly). Even my most recent war, where manpower was not an issue, was a reminder of the improved late-game balance versus EU3. As the Ottomans with my ally France, a war against Austria, Poland, Spain, and the Netherlands ended in a white peace, despite the first two having half-strength armies to start with. Civ lets you pick off civilizations one at a time; they actually make sensible and effective alliances fairly often in EU4.
And the losing money while at war part is intentional; one of the vanilla dev diaries specifically mentioned that it shouldn't always be possible to remain profitable while at war, and in Paradox's multiplayer sessions that usually wasn't the case. And it's true. In my last war, despite having a strong economy, I soon found myself facing losses every months with reinforcement costs of up to 75 ducats/month (and at the end, 140/month), and combined with raising new troops, took out 1500 or 2000 ducats' worth of loans. All while being under force limits. War ain't cheap anymore like when I had over 100,000 ducats to spare in EU3.
Also, that's an impressive Ethiopia. As well as HRE. At least from the political map, it looks like you were pretty successful for a second game.