I have been reading various threads on pregnancy and I have a few questions...
1) I know that diet changes should be avoided during the gestation period. However, I believe the poor thing will be on pretty crappy food and I found a good one (wooo!) so would it be better to switch?
I wouldn't hesitate weaning her over to a better feed even if she is pregnant. It can't hurt the babies and better nutrition will help her as well as the babies.
2) I heard that babies can be born days apart. I am guessing that a doe that is straining is in trouble. But if she doesn't strain is there a possibility of trouble or is it always obvious?
It's very unusual for babies to be born days apart... one of the reasons it was discussed here. Most does have the entire litter in about 15-20 minutes with no difficulties. Most of the time, you won't even know they are kindling (except that she is in the nestbox.)
Most problems will be obvious (but not all...). Straining will indicate a problem, as will excessive bleeding (I mean blood dripping/oozing out of the vulva). In either case, a vet will need to intervene. Most kindles are perfectly normal and the does handle it just fine. You will have to check the nestbox when she is done (after she leaves the nest, cleans herself and is relaxed). You can give the doe a little treat to distract her. Make sure all the babies are in the nest, warm and moving. (Remove any that are not...).
3) And can someone recommend a list of things that I should have on hand please?
I prefer to give the does a nestbox to kindle in (some people just give a nest of hay and straw). I keep a heating pad and towels in a shoe box, incase the babies need to be warmed or kept seperate. There is very little you can do for a newborn. Either they make it or they don't. The best thing you can do is make sure they are warm and quiet and the doe is comfortable.
Any other things I should know about?
Relax and let her do what comes naturally. The less you intervene the better for her. Move slowly around her and talk quietly, especially if she isn't used to you. Have patience, her hormones will be fluctuating for a couple of days. She may be protective and aggressive... give her time. She may not feed them for a full day after they are born. They have fat reserves that will hold them over. It may take 8-12 hours for the milk to drop, have patience.