A couple of things.
Firstly, if you stop your subscription and you have listings active still, then you will be charged each month when they renew and at the basic rate. (30p I think without checking).
A quick look though and you only have 43 listings active, which barely meets making worth having a shop in the first place. You need around 75 to make it worthwhile.
So why do you have a shop? If it's just for the shopfront, then you are probably wasting money. Unless of course you have a lot more listed normally.
Yes, if you stop your subscription for 3 months, you can restart it in October. But as above, it still won't be free. And yes, if you go in holiday mode and leave your shop active, you will still pay the monthly fee. But if listings are still active, you will pay every month to relist every listing.