Wouldn't trust used stuff. Figure out which helmet is comfortable, look at full face helmets first, but ultimately its what you deem more comfortable (I found the 3/4 faces more comfy, but still wish I got a full face). Also make sure it has the DOT sticker and if you have the money, a SNELL sticker as well. Jacket, your preference. Either a leather jacket or perhaps a Joe Rocket jacket (more expensive). JR's have built in armor and removable layers and stuff. Those run $300ish at my store. Gloves, Joe Rocket sells nice armored gloves as well (to protect the knuckles and such). Those run about $80 from what I've seen. For boots I would recommended a good sturdy pair of over the ankle boots. Thick jeans will be good, but even better are "Draggin Jeans", they have built in armor as well from what I remember, but also cost alot per pair.

Make sure your gear is comfortable and doesn't hinder any movement, someone at your local bike shop can help you fit stuff a lot better.