Whoo hoo!!!
Can't wait to see pics of the fluffy giants!
I never use heat mats. Especially on tomatoes. Tomato plants grow to be stronger overall when they are started at cooler temperatures. They germinate and grow quickly under higher temps but they are not hardened and don't do as well after being transplanted when they are started at the higher temps. I always try to start them between 55 and 70 degrees for this reason (house gets down as low as 55 at night but the seeds are under plastic so the temps are probably not quite that low and up to as high as 70 during the day). This, of course, is my opinion and you will find lots of articles that say 75 to 80 is optimum but this works quite well for me.
Almost all of my tomatoes are starting to come up now and so is just about everything else. At those temps. There are a couple of things that don't do well started at cooler temps but they are few. I'm going to try to find a website that talks about this. I have an article somewhere on this topic but who knows where it is right now. My old neighbor that started her plants in a greenhouse and babied them along complained to me about how much more fruit my plants had when mature. Her plants were huge as babies but did not produce well at all once mature.
Here's a short article that speaks of this but it is not anywhere near as detailed as the study I first researched on this topic.
http://growingredtomatos.com/
And you are correct on the vitamin deficiency as being one of the most common reasons for curled toes. The deficiency is present in the mother when she lays the egg. Another reason is an injury during hatch and/or too high or too low incubator temps. The vitamins (and splints) work best when the chick is just a day or two old but it wouldn't hurt to try it now Seth. Good luck!
http://www.avianaquamiser.com/posts/Chick_curled_toe/