So not only do you like fortifications, but similarly historical towns are among your interests too! We have something in common

I went to check out what the world knew about trolls and see if I could find a suitable suggestion for the town's name. It appears that these creatures originated from Norse mythology and further on examples are given of actual places that refer to them in their name. A plausible story could be that the cleric named his church Trollkyrka (or -kirke, meaning church in resp. Swedish and Norwegian) when he founded it and as the town grew around it, it became known as this.

The farmland question is something I have recently looked into myself as well and I found some helpful information on this page. There's a lot of interesting stuff written there that could give you some insight. As for structures that you could add, perhaps a type of barrier that is either already finished or one that is visibly under construction?

Am very curious as to how you will develop your story and the map!