No, stain free putty should not be used on ABS materials. Instead, silicone sealant is recommended. 
This warning is listed because the Plumbers Putty contains small traces of Quartz; however the Quartz is inextricably bound and cannot come out of the product, so as a result it is not harmful.
Maximum temperature is 250°F.
Yes. Always make sure that your paint is compatible with the Epoxy. This is normally done by contacting the paint manufacture. 
Yes. 
2 years from date of manufacture if the lid is sealed properly.
After the soldering process is completed while the pipe is still warm, you can wipe the joint with a dry clean rag to remove the excess flux. If the pipe has cooled or fluids are passing through it, you can use mild detergents (i.e. Dawn dish detergent) to wash off the excess flux. 
Yes. It is very important to stir upwards from the container bottom to insure any salts which have settled are mixed evenly into the flux. This should be done before the start of each project.
2 years from date of manufacture.
Less than 2%.