As Quilterella said, skip the 6500 ... there's so many more features in the 6600 over the 6500. I considered it when I bouight my 6600, and as soon as I saw the differences, I never even gave it a consideration. I love my 6600. One being the AccuFeed system ... you won't want to miss out on that!
I don't know the 7700 well ...as you mentioned it does have the extra 2" throat space, and it seems the free arm is important to you though, which as you know is not in the 6600. Take a good look at the options of the two .... I know there are a few things that are on the 6600, that are NOT on the 7700, that to me, steered me from the 7700. One I seem to recall is something about the thread ... perhaps, does not hold 2 spools? or does not allow for larger spools? Sorry, by I can't 't remember what! There's a good comparison chart re features on the Janome site.
As for the Juki ... sorry, I know nothing about it! However, to me, service is all important!!!!!!
Another consideration ... the Janome1600 is known to be a true workhorse for seamstresses. It only goes forward and backwards, no fance stitches, and I'm sure it has the free arm. So perhaps the 6600 and 1600?
It looks like your husband is giving you a nice budget to pick your "forever" machine(s)!! Take your time, compare the specs of each of the machines .... and go on in and do some test drives. And no, you are not overthinking. Rather you are shopping wisely.
Good Luck! .. and Have FUN!!!