I currently have a VIP 622.
1. Can a Joey be hooked up wirelessly, or does it have to be connected to the Hopper via hard cable? I have a wireless Joey and a "hard wire" moca joey. The wireless, surprisingly, is slightly faster and reliable so far (about 25 feet from the hopper through a wall). I wold go with wireless if your joeys are no more than say 1-2 rooms away from the hopper. I can't comment on the performance at longer distances.
2. Will my existing antenna work, or do I need a new one? If the dish has to be changed, how do the dimensions compare? Depends on what antenna you have now. You will probably need new LNB's at minimum. Online says dish is 36 x 6 x 24 inches, sounds about right.
3. What is everyone's opinion / pros and cons of buying the Hopper outright from Amazon or other retailer, vs Leasing it from DISH? I did the math for my situation and there was no financial incentive to buy my own equipment once I amortized the up front costs of buying and potential costs of repair/replacement. Your going to pay a monthly "outlet fee" regardless. Its hard to consider a situation where there is an advantage to declining "free" equipment UNLESS you plan on having the specific device disconnected for a significant portion of a 24 month period or you just cannot be under a contract for whatever reason. The Hopper is fancy technology that will get better quickly - most people interested in Hopper's features and technology are going to itch for the latest, greatest offering two or three years down the road, its cheaper to lease and upgrade.
Thanks