Hi Katie, and welcome to the forum.

First off, I think that would be a very nice anniversary present, which I'm sure your husband would appreciate. Let's hope he doesn't read the forum in advance!

Now onto the watch itself. I have one of these myself (third from left in the photo below):

so I can say that that example does indeed look like a genuine, original watch (bar the bracelet, as the seller comments). Mine actually came on a non-original bracelet too, which I swapped for the strap in the photo - it looks pretty good on a simple black, perforated racing strap like this.

The seller is asking the thick end of the market value for these, particularly as it's not on a Heuer bracelet. It's not a limited edition as stated, nor is it all that rare with date - 73453s were actually probably the best selling of these manual wind second generation Carreras, because of the extra usefulness of having the date over the 73353 and being a fair bit cheaper than the three register 73653. Still not exactly common but not as rare as the seller makes out either - I'd use that and the aftermarket bracelet to see how far the seller can be squeezed on price.