You got them right, Rudy. Ball valves are cheaper and harder to get fine control over flow. Gate valves are more $$ and easier to fine tune. Which you use on a reactor manafold has a lot to do with how much money you want to spend and how much of a control freak you are. Most of the parts can be had at any hardware store. Irrigation supply houses are good and usually carry better quality parts. They're also available online -- US Plastics or Bulk Reef Supply, etc.