Anyone got any tips for a beginner? Like what's the easiest class to start with?

The games is quite long, so if you're like me you'll only play through it once. I played a a mage, I found it quite easy. The ability to immedately wipe out their danger units gave me a huge advantage, and I was often able to beat odds which the difficulty rating said was impossible.

Mage is probably the most powerful class in the first game, and also offers the greatest variety of tactical options. As for additional tips, weigh each battle before entering it, remember that discretion is the better part of valor (most areas have a few very strong troops you'll need to leave alone until later when you're stronger), and once you purchase the reserve army slots it's worthwhile to keep a few alternative troops on hand to switch out depending on your enemy (for example, you'd want to switch out archers for priests if facing skeletons, or switch in green dragons if facing black or red dragons). Other than that, just don't be afraid to experiment with various troop formations and tactics to find out what works best for you.

Make sure you do the first couple of king's quests early.