One important thing would be that a personal union between Lithuania and Muscovy doesn't immedietly mean that it will be succesfull - you can't simply assume that it would lead to a "Muscovy is stronger" or "Lithuania is stronger" scenario. There would be internal conflict between the two states which would have to be dealt with - do remember that it took often took centuries for states to merge their personal union's to real one's (the PLC being and obvious example here). It may very well be that such the two states would descent into civil war, or become a target of their neighbours - Poland, Sweden, Turkey, Livonian Order even. And there is Novogorod to be wary of.
On the other end - Habsburg Poland would indeed be intresting. Does anyone know what was the status of the various Silesians Duchies at the time? How many piasts were there? I imagine the Habsburgs could try to legitimize their claims to the polish throne by having issues of Jadwiga and Wilhelm married to those various dukes, in Pommerania as well. Also, IIRC while Silesia was out of polish control at the time, according to feudal law at least some of them were part of the "Crown Kingdom of Poland" and only legally surendered to the HRE during the First Congress of Vienna. So how much could Poland realistically expand westwards? And could it be possible for it to become a part of the HRE the same way the Kingdom of Bohemia was - with election rights, broad autonomy, etc.?