I think the temp thing may have to do with breaking up of the fats. I don't think it necessarily makes the milk "bad," it just isn't preferable.
Have you ever used room temp butter and cold eggs to make cookies? Once you cream the butter and sugar together, they're all happy and fluffy. Then, you add in cold eggs and suddenly, everything curdles and separates. The reason this happens is because the coldness of the egg makes some of the butter reharden (i.e. get cold again) and causes a separation of the emulsion. My guess is that the same thing happens when you add warm to cold milk.
As for adding cold milk to frozen milk, the cold milk will actually bring the temperature of the frozen milk up above freezing as well (thus unfreezing it). However, maybe the LC recommended it as the temps are close enough together that it matters less. I'm just guessing on that though.
Fresh BM is good in the fridge for 6-8 days so you can hold several days of pumping before freezing. That's what I do. Like Biddy, I mix bottles of cold expressed milk to make bottles for DS. Since I EP, I tend to mix "morning milk" with milk from other times of the day before freezing it. "Morning milk" (i.e. my first morning pumping) is the most plentiful and is also high in foremilk and low in hindmilk. You gradually have more hindmilk throughout the day, with the most being from the last pumping of the night. So, I tend to mix my morning milk with other higher fat pumpings before freezing so my freezer stash is more even on fat distribution.
I also agree about pumping after your first morning feeding. As an EPer, I can tell you that pumping and feeding at every feeding is an insane amount of work and if you don't have to do it, then don't. I'd try one pumping session in the morning and only add more if you need more milk. You also have to remember that your baby is much more efficient than the pump, so even if you feel like you're tapped out, the baby can still likely get milk out. I completely stressed over this in the beginning and wish I'd taken a more relaxed position on it.
In case you haven't already checked it out, this is a great site for BFing info. www.kellymom.com