Did you just get hired by OnMarket? You have gone from...

Did you just get hired by OnMarket?
You have gone from diligently trying to figure out how to make this an effective strategy/product to sounding like you are doing their PR!
Must have been an interesting email you got.

If you can only take money out once a month (without costs), it means you can't defund the ones you don't want to participate in.

This could be an outstanding product/strategy, but it doesn't sound like its going to be given the number of concurrent SPP's and the lack of flexibility to participate significantly in the ones that will make you the most money.