You can create variant (legs) with different options that can be selected on the sale order. Since you wish to have inventory separate for legs and board, you would need a BOM defined for it.

Create product table as storable with variant options. For the product table, define a BOM with 1 board, 4 straight legs, 4 curved legs etc (all the variants). For the legs on the component line specify the variant on the "Apply on Variants" field.

2 Options

1. Mark he BOM as a KIT .. this would mean that you deliver Board & legs separately, 2 lines on delivery Order.
OR
2. Mark the BOM as Manufacture this product, this option would create a Manufacturing order each time there is an order for this product. You would additionally need to include MTO route on the product's inventory tab.