I would say you can start buying PSAs at the start of your SFI business if signing up PSAs is a bit difficult for you to do I know it is not everyone that is good in talking to people face to face
Another way you can make this easy to do is by setting up standing order of S-Builder co- op they are in units so you can choose the units you will be able to avoid monthly with this you are sure of having new PSAs each months