You have got some confusing information here. The 28 mentioned in the review is not the 28.5 which is an entirely different boat. There is a Hunter 28.5 forum with more info on the boat. Hunter 28.5
The price seems a little steep at $20K. Depending on the condition price should be between 12 and 18 K. I would imagine a boat in Miami would have the usual salt water and sun ageing conditions.
2 weeks from Miami to New York on the ICW is a little tight. Since you are only running in daylight that means about 100/mi day which probably is not realistic at 6knot motoring speed, waits for bridges etc. Obviously the Yanmar 2GMF-20 needs to be in top shape with a recent oil change and new filters, the shaft aligned and the engine aligned. The bottom should also have been recently painted and clean for the trip. You also would need some engine spares to be safe like primary, secondary filters and belts. My guess that your plan would be a touch ambitious with an untested boat. You could go offshore for stretches and with the right weather window and Gulfstream conditions you could make it. I wouldn't with a boat new to you. Too many things can go wrong with a boat that you don't have experience with and an intimate knowledge of its history.
I've sailed a Hunter 28.5 and they nice performing boats although not up to offshore conditions. Gelcoat cracks at the chainplates and stanchions are pretty common. Additional areas of concern are the cast iron keel and deck compression issues due to leakage around the wiring at the mast.
For the money you are looking at I'd also look at some better built boats C&C 29-2, Cal 28-2, later model Sabre 28, Tartan 28, later model Catalina 30. Pearson 28-2.
You might even consider a freshwater (Great lakes) boat and pay to have it trucked. You will save a lot of time and money in the future not having to deal with some of the ageing issues common in saltwater boats.