I just spoke to one of the companies that gave me a quote. He indicated that he would run the Manual J numbers if/when I commit. I pointed out that I have most of the room, door, window, and ceiling measurements already and he said he could run a quick calculation but he is very confident that it will match what he has estimated.
I also found a spreadsheet on the ACCA site (https://www.acca.org/Files/?id=128) and i might try plugging the various numbers i have into the spreadsheet to get a sneak preview (assuming i'll be able to make sense of this). From what I can tell so far, it appears to be based upon the abridged edition of the 8th edition of Manual J so i can't judge whether it will be a reasonable approximation of what a skilled professional will generate using the full calculations but worst case maybe I'll learn something?
I have one more company that I've just emailed that appears both on the NATE and ACCA lists and has good BBB and angieslist ratings--I'm not sure how I didn't see them before. Hopefully I can get them to come out in the next week or so. I've taken dash's advice and have asked if they will do Manual J, S, and D.
Speaking of which.. are all three 'must-do' for my situation? I hadn't really heard of either Manual D and Manual S prior to dash's reply.