I don't want to give a harsh review to what is obviously an early effort by a novice map maker, but I'll point out some things that might make your next effort a bit better.
As on another map I recently reviewed, its evident you used the biggest brush size for almost all your terrain elements. Try using the smaller size for a more natural look. The hills and elevations are just plopped here and there, you might want to try using the 'equalizer' tool to make your landscape more rolling and natural instead of flat with hills evenly spaced.
The layout is very unnatural throughout, it almost looks like a sampler of the various terrain types and structure types. Starting with the terrain, you would look at your basic terrain treatment before you start your castle. You must admit what you have there is very unnatural. Try grouping common types, like, make a river, the marshes would go in the wetlands, the river would flow from high-ground to the low ground, where the marshes lie. Make valleys and glades between hills and highground, and decorate it with appropriate trees and bushes, for instance one method is putting pines on the highground and fuller trees in the lowland forest glades. None of these rules are hard and fast , they are suggestions on one method to make it more natural looking, rather than just randoming using all the land types without rhyme or reason. Then you start placing buildings: farms go in the fertile rivervalley lowlands. Crafts go nearer the castle, typically within the keep. I think if you consider, you wouldn't put 4 chapels together in a square like that. There is an in-game use for chapel and church, blessing the peasants, so naturally you want to spread them out because the priest walking by a peasant is what gives you blessing values. Put one near the stockpile, or town gardens, or the granaries so the priest will encounter workers. (not to nitpick, but with that big a population you'd want churches, rendering all those chapels unnecessary) besides the fact it looks more realistic to have the chapels spread throughout your 'county' instead of squared up in a cube like that. That goes for any town building.
On your castle walls- the sawtoothed walls, as you may know, are crenulations. these offer some protection to your archers. Now of course there are scenarios that leave the outer crenulation off and require you to complete the castle before invasion, but your land type usage makes it impossible to put crenulations around a lot of the castle. This is unnatural looking and not very useful for defense.
A lot of your buildings and landscape is crowded together in one section of the map and a large section has very little- try spacing things out a bit, and I'd suggest moving the signpost farther from the castle. The way it is now, one quadrant of the map is completely irrelevant to gameplay.
A suggestion on Scenario- you have allowed Trading on every weapon. This basically makes weapons crafts unnecesary, especially when you have so much readily available resources for sale, (stone and wood). For more of a challenge turn off some of the Tradable Goods.
These are just suggestions and this is meant as constructive criticism. The map has potential and if you do some detailing work and put some more thought into the use and purpose of the various buildings in making your map more challenging you may have something there.