Six filters is plenty in most cases, especially if you have a separate equalizer for the subwoofer.
There is no mic for the YDP, you have to set it manually. However, using REW’s RTA feature it’s pretty easy.
It’s no problem finding them on eBay here in the United States; not sure where to tell you to find them in New Zealand. It’s a legacy product; they are only available used.
Try to find one that was used in a permanent installation, not one that was used for tours or rentals. An easy way to tell the latter is that they often have lots of scarring around the rack ear mounting holes, due to being often moved from one rack to another. Another clue to look for is bent and/or cracked rack ears. The unit is fairly heavy with a deep chassis, and the rack ears weren’t strong enough to support it unless it was racked on top of some other component.