Oh... so many quesions to answer , by everyone 
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Sure, just as Zelenskiy must "declare victory" in any outcome whatsoever, and Trump and EU must all "declare victory" in any outcome whatsoever. So everyone must claim to be a winner! For Putin, no NATO in Ukraine, return of Russian culture, language, books, religion etc.. in Ukraine, 5 new territories I believe would be an easy sell. Plus it sets a precedence, do you think Georgia or another buffer state would accept Nuland's cookies now seeing how much Ukrainians had to pay for those cookies in blood and territory? Also, don't forget the agreements between US and Russia are not only shortsighted to stop the immediate guns from firing, like I've been saying big game is played for spheres of influence, and voters in Odesa and Kharkiv will be the most problematic and become huge liability for current regime in Ukraine.
Demilitarise - of course vague from the start on purpose, but if Ukraine will become a neutral state and not under any military alliance like NATO, I'd argue that this point was achieved.
de-nazify - i believe the most aggressive nazi's that wanted to fight Russia the most, did so first and are no longer with us. Azov one of the most radical groups with literal Black Sun in it's logo is now just a shell of itself and was integrated into official Ukrainian army and removed the Black Sun. After the guns are silenced it be hard for wounded nazi's to get new recruits and those that are not wounded would be a laughed at as they retreated from Mariupol and left most of their comrades there and then retreated from all of Donbas. It's hard to sell yourself when you retreated. Plus with Russian culture and language the victory day and Ukrainian role in defeating Nazi's would also come back to the masses, and Bandera and right sector would be tabooed.
We're yet to see what will happen to the Ukrainian regime once guns go silent. This would be the next step, and it's impossible that it wasn't part of the agreements discussed by Putin and Trump
Russia was only asking for Donbas (2 regions) before this all started, plus I'm sure Russia will publish US's written response to its security demands that it received in January 2022 before this all started.
Not taking Zaporizhzhia and Kherson (cities) would be a huge minus for Putin, but if Putin gets everything else i believe Russians will be able to overlook it
Of course i do not have any insights on the terms of the actual proposal. But if in it Putin didn't get those things, like if Russia had to hand over Kherson Oblast to Ukraine, or Ukraine was allowed to join NATO, or Russian language didn't return to Ukraine, then selling it as a win for Putin would be much more problematic.
If Ukraine won't be neutral and is allowed to be armed to the teeth including nuclear arsenal then i will concede that it will be a loss for Russia.
But i think you're doing a great job prepping the ground and claiming this as not a win for Russia. If Russia gets all those things i talked about and you can somehow sell it as not a win for Russia, then i'm all for it.
I do not think that Zelensky has to announce a victory. Remember, he is actually an elected president. I doubt very much he wants to stay in power (I would not).
Return of Ruzzian culture... I do not see how that is going to happen. Ruzzia now is hated - as you would imagine.
New territories (5??), maybe. But you have to ask what did you exchange for them and how long will you be able to hold them.
No NATO... well, formally that may or may not be the case, but after this war, Ukraine will be permanently in war footing. No more "surprises" and if Ruzzia wants to try again, it will find something completely different. I think Putin and the future gangsters of Ruzzia understand the real cost of invading.
But again, all this may or may not be. I do not picture Zelensky giving territory for free and I do not picture Europe taking just any deal no matter how bad. After all, US is no longer a trusted ally, so if there needs to be confrontation, there will be confrontation.
The Ukrainian elected president's term ended in March 2024.
If Russian language and religion is not returned to Ukraine then it won't be a win for Russia.
Crimea, Donetsk, Luhansk, Kherson, Zaporizhzhia. As I've been saying multiple times, it's not about the land (Russia has plenty) and it's not even about Ukraine, but about spheres of influence and Russia's position in a world order. EU needs Russia's resources, if Russia comes out independent out of this then it gets to decide who in EU gets it's resources and on what terms. At the very least I can imagine things like factories/manufacturing closing in Germany and opening up in Hungary or getting outsourced out of EU completely. Every time you take a strong position, there must be consequences if the outcome is not in your favor. Russia has resources, Europe needs resources, there's no way around that. They can purchase "freedom" gas/oil from US but only temporary as it's just simply not sustainable. But Trump never said that he's going to make Europe great.
Without Ukraine agreeing to stay neutral this will not end. Plus being on war footing is very expensive, directly and indirectly. Who will pay for that, and what will happen to whatever population Ukraine still has left? Plus once martial's law is lifted people will get to decide whether they want to build factories for guns or butter.
It appears Ursula/EU is pushing Zelenskyy to fall into Trump's trap. If Zelenskyy doesn't accept Trump's terms today, Ukraine will just loose more people and more territory, then it will be impossible for Z to accept peace on even worse terms. The only possible outcomes if Z doesn't accept agreement today, will be either full capitulation in Ukraine or collapse of Russia.