I play on hard and try to average one captured settlement each turn. You can expand fast if you don't fight on too many fronts. Try to eliminate enemies completely by picking on enemies with a small number of settlements first. 

Start settlements with growth and public order buildings that you will replace once you have a chance to upgrade the main settlement building. Consider building a lord and some heroes that buffs public order/growth/income and moving them to newly captured settlements while its suffering the initial debuffs. They can also crush rebellions.

The best way to earn money is by winning battles. After you win, invest that money in as many money making buildings as you can fit in your settlements especially the unique trade goods. Upgrade settlements as soon as you can too. I tend to have one or two recruitment cities and everything else making money.

Actively seek trade deals with factions you don't want to fight (yet) even if you are making 80 and they are making 350 that is 80 you didn't have before and as you expand you will find new trade goods.