high humidity can be a problem
mold can eventually thrive on the package and glues and cardboard center.
the mold won't directly "feed" on the vinyl but will still destroy it
Heat can be a problem, but if it's less than 105F I wouldn't worry about it.
eventually, but not on a short time scale
Not sure, all my vinyl are in their covers and in cases, seem to be OK.
Humidity is not the best thing.. Over time it might have some effect depending on how bad it is.. They should not get wet and humid. That could ruin them. If you are nervous about it, there are these.. Hmm, what are they called in english... These things that clean them :).. Anyways, cant you just put on some ventilation around your records? Damn my english sucks today.. Im talking about those airblower ventilation things.. That would probably help.