As stated above, check with county health. A dry seasoning mix will likely come under Cottage Industry classification initially, and you would be fine. Anything wet or requiring cooking during preparation, or that you wish to sell through retail stores, you will need to use a commercial kitchen.
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If you plan on selling more than a few cases a year, you really want the help of a co-packer, as they can get the lab analysis, UPC code and label design approved a lot easier than you will be able to.
In terms of spices, use spices from a large supplier with national recognition, my favorite is Penzey's for quality. The issue will be that if you choose to go to a co-packer, they will always have access to different ingredients than you do, and they will always want to reformulate to match their processes. If you are going to process at home, definitely get a business i.d. number (tax payer i.d. number) and a business license and buy your ingredients from a local restaurant supplier with good turnover.
