Listings renew every month @pressbs4. Every listing counts towards your 250 free insertion and once that's exceeded you pay per listing.
As of Feb 1 if you have 350 total listings, you are 100 listings over your free insertion limits and you will pay insertion fees for those 100 listings.
The non-store insertion fee is $0.35 per listing. You're looking at a total $35.00 insertion fees each month if you carry 350 listings.
At that price, it would be less expensive for you to subscribe to a Basic Store which is $27.95 / mo for a monthly subscription or $21.95 / mo for an annual subscription. I suggest starting monthly for a few months to make sure you want to continue with it. Early termination fees on an annual subscription can be significant, while a monthly subscription can be ended without penalty.
The Basic Store comes with 1,000 fixed price free insertions, 250 auction free insertions (in select categories only) and 10,000 additional free insertions (in select categories only). The extra 10K does apply to crafts, which you've listed a lot of, so that will help as you grow your store.
Edit to add a link to the stores fee page:
Once you subscribe to a store, the store listings will override the 250 free for non-stores. If you subscribe to a Starter store you get 250 listings - not 250 + 250. This is why I recommend starting with a Basic subscription level.
