Its obviously entirely up to you as its your game, but I think you'll find if you manage your battles properly, you can acquire the more "expensive" promotions fairly easily with a barracks/stables and the correct civics.
Great generals also help a lot.
If you're still having trouble an aggressive leader (combat 1 to start for some of your units) will also give you a head start.
But as I said, you bought the game, do what you like with it.
Just expect some abuse from some posters for changing the game to make it "easier"