Need help making first dungeon

Basically I don't know if my dungeon is really good enough, like I don't want to make it too hard. My players, which are 3, are currently level 2 and trying to get a gemstone from the cave to unlock a door. Well right now there is a cult tryin to do the same thing. The enemies are 5 cultist and then the "boss" Is a ghoul. I also have a puzzle that the players have to do to get into the room with the Jade. Is this too much? Also the reward I was going to give my players is basically a D4 they roll and it turns out to be either a: Boots of Striding and Springing, Goggles of Night, Cloak of Protection, or, Weapon of Warning. What can I do to change it up I don't mind changing the gear or enemies I just know I want a "boss". Also should probably note my players are a cleric, paladin, and warlock.