I was considering reducing the number of huts in a pile to 5 to reduce the length of the game (4-players seems to take a while (especially with new players). Should I take out some of the civilisation cards too or would this mess with the balance of the game too much?
Personally, I think teaching new players "house rules" can be a recipe for disaster. Make sure you inform them of the changes you make and the reason for them.
To add something constructive. how about each player starts the game with 2 wheat fields and 2 tools, that could also speed up some of the early part of the game. You could even handicap yourself by only taking 1 or 0 of each at the start or some such.
Taking out the civilization cards will surely mess with the balance of game. Its multiplication factor is the ROI of what you did in the game. If you invest more manpower in weapon crafting you can scroll point from them using multiply factor of weapon point in civilization card.
The civilization card give you the hidden point until end of game. Hut give you disclosed point. You can knock out your opponents at the end of game with those hidden point. That is really fun.
My group reduce the number of huts in each pile to 4-5 and also eliminate those huts with face of "1-7 resources" out of the game as well. The hut card give too much point when someone buy it with 5-7 golds (30-42 points). It's too hard to catch up the buyer's point in shorten game.