If you are looking for just one humidor my opinion is that you have to go with a tower that claims to hold at least 2000 . You'll get room for your goal of 1500 and enough room and shelves / trays for both boxes and singles. It won't be too packed and therefore allow better air circulation.
My guess is you'll have to spend a little more than your budgeted amount but there are some good deals are out there on good quality towers. You'll also need a good humidification device and fans if they are not included in the deal.
If I lived in the US, I would have bought one years ago but here in Canada, the towers cost more than double their US price and shipping is just a killer so I am still waiting on a deal and use my many Coolerdors, a Wineador, a few wooden desktop humidors and a few Tupperdors.
I do have to say that keeping RH and Temp levels stable and steady is easiest with a Cooler than with any wooden solution I have tried though. And I have tried many, even very high quality desktops just don't even come close. It's not pretty and you probably would need maybe 3 big coolers for your needs but they are cheap and efficient. It costs me roughly $200 CAD for a big cooler with Heartfelt beads, Spanish cedar lining and about 10-12 SC trays for singles. They are much less when putting one together for boxes since you won't need the trays then.
Hope it helps a bit even though I don't consider myself a Senior BOTL as there are many here with much more experience and I don't just mean they are old