I would like to clarify whether the depreciation allowed under Section 179 is in addition to the regular depreciation.
No, it is not. If you fully depreciate the item in the first year under SEC179, then you are done with depreciation of that asset totally and completely. Generally, using SEC179 to fully depreciate an asset it's first year in service only makes sense if you have the taxable business income in that year, to claim it against.
