If I destroy my alliance fort will I get resources back and will a new fort need fewer resources to..

Destroying a fort or watchtower does not refund any resources. The fort resources are based on the level of the Fort. There is the main - which is the cheapest. The next two, Fort 1 & Fort 2, increase in required resources.

Note: If you destroy your main fort without another fort nearby any watchtowers will be "expired" and you will not collect any alliance resources from any alliance nodes within the areas of the expired towers.