There are other advantages for unique identifiers, like detecting/counting collisions on a particular TriMesh for example. It's good practice to use unique identifiers, you may not want to move static objects but you may need to access them for other reasons. If you design your code in this way from the outset, it'll save you a lot of editing later on if you suddenly realize you need to access them.
Regarding the second question, whether you use an array or types would probably boil down to personal preference and its application. For a LOD system it may be easier using types but you could still use an array if you wanted to.
Regarding the second question, whether you use an array or types would probably boil down to personal preference and its application. For a LOD system it may be easier using types but you could still use an array if you wanted to.