I trained Standardbreds for the track for over 20 yrs and now train alot of minis.
I highly recommend you get someone to show you. The harness takes a bit of practice to get used to how everything goes together and how to properly adjust.
I also HATE metal easy-entry carts. They ride rough and don't hold up over time. They are also quite uncomfortable unless you're on a perfectly level surface. They're 499 because that's what you're getting, a cheap cart.
If you really want to get into driving, get your horse trained by a professional and get a nice used Houghton cart or other well made cart. Your driving instructor can recommend lots of other companies that make well made carts.
Have fun. Hafies are one of the easiest to train to pull.