I don't think that Prussia will get Saxony as Austria would oppose that, not even the part of it like otl . I believe they will more, or less get back their Polish territories , also given that we are speaking about Frankfurt Congress that probably means Napoleon accepted Frankfurt Proposal and given Russian marriage and potentially better communication with Tsar, plus the fact that Austria was open about French natural borders (out of quite different reasons as they hoped to have France as counterbalance to Russia, but without Russia they can't really continue the war, especially not when they have already secured everything they possibly could).
This also means that Prussia doesn't get the Rhine and given that Russia had lesser role to play in defeating Napoleon and was even supporting him its quite likely that Prussia gets its Polish territories together with Austria, plus Westphalia region as Matternich and Austria would still want Prussia to have border with France , plus otl there was also deal with France on this one during Napoleonic wars.
Russia probably comes out with claim over Finland.
Otherwise im surprised that Ottomans didn't seek abolition of Russian rights to Protect Christians in Ottoman Empire? I would imagine the congress being a good chance for it.