Yes. Hosting the ARPA zones for your own IP ranges in Azure DNS is fully supported.
Simply create the zone in Azure DNS, then work with your ISP to delegate the zone. You can then manage the PTR records for each reverse lookup in the same way as other record types.
You can also import an existing reverse lookup zone using the Azure CLI.
Hosting the ARPA zone for your ISP-assigned IP block in Azure DNS is charged at standard Azure DNS rates.
Yes.