#8 dust seal and #14 piston seal are all you need to rebuild, just clean everything out really well. You may need to clean out the seal grooves with a dental pick type tool to get all areas cleaned out. Lube everything with new brake fluid and reassemble.
Stainless brake pistons are a good choice if you need to replace the pistons you have. Your old pistons may have pitting that can can cause leaks, chew up new seals, and prevent them from building brake pressure. Stainless steel will have a longer life span.