First question:
Regardless of the context (commercial or private), for your website can be built with standard licenses (if you select premium images, the cost will be higher).
See here for more information:
License information and Terms of use | Adobe Stock
Second question:
A subscription is find when you need on a regular basis stock images. There is no need to consume all credits of a months allocation as they roll over to up a year of image credits. So a 10 images / month for a year minimum is interesting if you need around 120 images per year. For peaks you can even overshoot your allocation but that will generate additional costs. A subscription is only handling standard licences(no premium, no extended) for certain assets (no video). Premium, extended and video generate additional costs.
Image credits are useful if you have only an occasional need for stock images. Please note that the credits need to be used in between a year. With image credits you can also buy video and extended licenses.
If you have only 8 images, why not using the free test drive (10 images per month, first month free). However do not forget to cancel after the first month or you will have a subscription for a year at least.