I'm finding the early game really challenging, it's so hard to get a big enough militia to actually counter raiders,

Try getting your church up quicker, it'll pump you above 75% approval so you get 2 families moving in per month, also don't upgrade to burgage plot 2 until you need artisans

farming takes forever to make a decent food surplus

Sounds like you're on poor soil or using tiny plots, farming is super good if you have the manpower for it

trade is too damn expensive to get going with how expensive buying routes are.

The two trade development ideas (limit route to 25 gold and -10 to all import prices) are both must haves, if you're spending your first two dev points elsewhere you're wrong