in Dis the save has te be amde only once per hour in game time, so combat will be unaffected, it would effectively only affect travel time.
As for the burden system, again, once per hour you take the willsave (same as previous). Only when you fail the willsave you need so make a fortsave. the willsave DC's aren't that steep (at the start at least) i forgot to mention however that receiving a burden will reset the willsave DC. I didnt settle for nasty effects because the devils etc here are allready enough on the party to handle. It is only when you remain longer on this plane then neccessary. As for the month out of baator is indeed quite steep, ill rewrite it to "when outisde of Baator you will lose a burden at a rate of 1 per day."
remember this is for high level players... then a save DC of 30 is a challenge, anything less is just cake. assuming you save on 25 75% of the time and 50% on 28 you will take 7 hours to reach the 50% chance line when you fail then you will need to beat a DC of 20, wich is easy...also, notice you will need at least 4 burdens to reach a DC of 27 (again close to the 50% chance line), so extrapolating for that you will need to remain in minauros for 4*7=28 hours ingame time to start crying. Also, this is abilitydrain, nog damage, so it won't heal as easily, besides, the effects stack so yeah, that is nasty. Fortunatly the solution is on the next layer. I could turn the penalties for crying into a 'roll a d6 to see what you get' type of thing. the hp drain and dmg are supposed to be trivial.
the effects you mention are not that heavy. Penatlies on skills are next to worthless since high level party (15-20 and beyond) will have either had a great many skillpoints and thus not notice the effect, or won't use skillpoints anywayso they coulnd't care less. Diplomacy is broken as hell (even with the Rich Burlew rules, which I could autosucceed on a rushed check by lvl 6), so that wont actually be interesting. Penalties on attack is actually only bad for martial classes, and stat drain is hazardous for everyone. A fighter could actually take the con drain a bit, but a caster will quickly lose his con and woudl fear for his life, reverse so for mental stats. The paranoia should be roleplayed, but when he loses his mind, he will turn on the party potentially destroying the party, or at least damaging them.