Also I've solved Stronghold I.
The proper way to play (at least assuming you have some time) is to set taxes to low, switch between normal and extra rations, ignore any other intervention for popularity and increase your population. How far? Farther. Still? Yes. More people. Still more, really? Yes. STILL more? Did you cover the entire map with food production to the point that feeding more people is impossible because at last travel distance sets a hard limit and more people won't feed even themselves if they work on more food production? Then you can stop. If not, increase your population.
The basic design flaw is that raising taxes has linear cost but far sublinear returns, so there is no reason to raise taxes above low ever. On the other hand, increasing your population has linear gains until you run into the hard limits of space and travel distance, and also linear cost which is always much lower than the benefit, so there is no reason to ever stop growing your population until travel distance begins to matter.
What units you buy is comparatively irrelevant. Walls and everything related is useless if the game is played against a human. If you play against the computer, you need them for the first attack but after that your economy should be so massive that you can outproduce them on the hardest difficulty. If played properly, anything after the first attack is a total joke.