Yes, you need a valid category B driving licence. The passenger doesn't need a licence, and minors can ride as passengers with an adult, according to the operator's rules.
Closed shoes, sunglasses, sunscreen and a light sweatshirt out of season. On dirt tracks the dust is real: avoid light-coloured clothes you care about. Helmet and briefing are always included.
Yes: you start with a briefing and a practice stretch, and the guide leads the group at an accessible pace. For trekking, check the level shown in the listing: most are easy or medium difficulty.