Hi David,Sorry for a delay in response.Yes, you may use a Stock image in whole or part as a background or element in your own work (to enhance a portrait) provided you follow all the terms and restrictions of Adobe Stock. Please see Stock Licensing & terms FAQ: Where can I find the terms and licensing information for Adobe Stock? for more information. Also, an extended license will be required for this scenario.You may use the final image on social media/ website for the promotional purpose but ...
You may use the final image on social media/ website for the promotional purpose but a wiser approach will be to add a credit line to the photographer. If the images are modified the credit line becomes optional( provided the modifications are major).
Yes, to sell Adobe Stock images you will be requiring an extended license.
You can use the same license twice, however, please note that if you want to use the same asset for different clients, the asset must be licensed separately for each client use. Since the license cannot be transferred to someone else's authority, you would have to download a separate license for the subject's use.
Hope this information helps!
Feel free to update this thread in case of any additional questions.