Should i build a network of airfields?

It depends whether you need the planes quickly and whether you expect them to ever have to traverse that path again. If it's a one-time move and there's no rush because you're staging somewhere else I could see an argument for just driving, but the time-saving is often crucial if you're using your airforce regularly and might need your planes to respond to a fight on the other side of your territory. I almost always build the network unless it's something like a European map when I've started in and conquered North America, where I might just drive my planes to the ocean because they'll never be coming back.