Perhaps Klook isn’t the best source for transfers in Sapporo. On my first quick search for a local taxi company with large vans, I found this firm quoting around ¥18,500 from the airport to central Sapporo (about 50 km) in a six seater Alphard:
https://grandresort.jp/lp/...
If your hotel is only about 10 minutes from the airport, a regular taxi should cost less than that. Much less. Perhaps you could email your hotel and ask if they can arrange transportation for you.

As for the coin lockers — I can’t speak specifically for CTS, but at most airports they do fill up during peak periods. You didn’t mention your dates, but winter in Sapporo (especially weekends, ski season, and the Snow Festival period) tends to be busy. Arriving in the evening and needing multiple large lockers might make it harder to find enough available at once, so it’s worth having a backup plan just in case. IIWY, I would check lockers and if you don't find them, get someone at the airport to call for a large taxi.