I am trying to replace a door and would like some general advice from disinterested parties such as you all.

The door in question is between a fair sized, uninsulated entry area (about 10 x 10) which has the "real" door to the exterior (steel with a stained glass insert). The door that is being replaced leads from this area into my living room, so from an uninsulated to a living area. The current door is a nice wood stain (probably really wood) with an oval medallion made of glass. The glass medallion, which I have never liked, has been deteriorating for years and is now nearly ready to fall apart.

I priced getting the medallion replaced - $500. For the same cost, I might be able to have a new door installed. However, the current door is 35 x 79.5", not the standard 36 x 80".

I understand fiberglass offers the best insulation, and if I can do it fast enough, there is a small tax credit. However, can fiberglass be cut down by a whole inch?

Exterior wood doors are substantially more than fiberglass doors I have seen. However, they are not insulated. If I am going to get a wood door, how much difference in insulating value would there be between an exterior and an interior wood door, each with a glass insert?

A salvage place does have reasonable priced steel exterior doors with the frame. He says that if I buy the frame as well, it won't matter that the current door is slightly smaller than the standard. I understand the insulating value of steel is between fiberglass and wood - at least that's what Home Depot tells me about their doors. The salvage place just has the doors, with no technical info about them ( no warranties or anything).

The Home Depot guys seem very confident - but that doesn't always mean they know what they are talking about. The salvage guy had to ask someone else. So I thought I'd get some other advice. Thanks!