Thank you for contacting Aspose support.
All Aspose for .NET APIs can be used together in a single application because they all have dependency on .NET Framework only, therefore if you wish to use Aspose.Cells & Aspose.Words in your project there will not be conflicts. However, you must consider using the fully qualified namespaces to minimize any confusion for similar named classes/object. For instance, all Aspose APIs have License class in common, therefore you must initialize the License classes for Aspose.Cells & Aspose.Words as follow.
Aspose.Cells.License cells = new Aspose.Cells.License();
Aspose.Words.License words = new Aspose.Words.License();
Regarding the other part of your inquiry, you have to first check if your existing license is valid for Aspose.Cells API as well. You may check this by opening your license file in notepad, and look for the tag. If you have purchased Aspose.Words subscription only then you will not be able to use the same license for Aspose.Cells API, regardless of it's expiry or component version. However, if you currently own an Aspose.Total license then you can use the Aspose.Cells API that was published within the subscription period of your license. Please note, each Aspose license come with one year subscription that allows you to upgrade the API to any version that was published within the subscription year.
Please feel free to write back in case you have further concerns.