Hi Lee, Don't waste your money on boost .... you'll be surprised how fast a used filter will restart

somehow I don't think all the bacteria will die off by just letting it sit and once you start to re-feed the bacteria - the filter will start doing it's stuff.... I'm not suggesting you wont get new pond syndrome, just saying that boost is a waste and a used filter should kick start itself quicker than a new one.
PP on K1, is used to remove the coating left behind by the manufacturing process - some people swear by this. My experience was different, I fit it and forgot it, it cycled in about 6-8 weeks and has been going non stop since.
With a used filter, I would not see a need to PP - unless it's one you bought used and wanted to be sure that everything in it was
dead and everything sterile (if it's yours that was on the pond before PPing is not necessary), the process is to add PP to the filter filled with water ensuring the water stays purple for an hour or two (quantity is irrelevant, just add so it stays purple - not brown, if it goes brown add more PP), then drain to waste, wash with clean water, refill filter with water add some dechlor, sit for 30mins, drain and filter is ready for use. The whole process is done with the filter either not fitted or isolated from the pond.
Good luck