128
There is no limit.
No.
No.
Yes. After sharing an image with other tenants, you can still use the image to create an ECS and use the created ECS to create a private image.
If you have rejected an image shared by another tenant, but now want to use it, two methods are available:
Ask the image owner to add you to the tenants the image is shared with. For details, see Adding Tenants Who Can Use Shared Images.
Accept the rejected image again. For details, see Accepting Rejected Images.