Hi KenTheBeast!
There are free slots on the Town map. Select them to open the Construction menu, where you can choose a building to construct.
There are two types of slots. Depending on the slot type, the Construction menu displays two different lists of buildings:
You can find full information about buildings that can be erected in your Town here:
https://vikings-support.plarium.com/web/en/guide/buildings/slots-for-building
Hope this information will be helpful! 🙂
You can build manors, which produce silver.
Yes you can have a forge, several buildings are already there when the game starts, I cant remember if the forge is one of them.
No you cant build a gold mine, fortunately, at the moment, gold is not so difficult to acquire if you know what you are doing and put your mind to it.
Mining gold is very slow