You don't need to purchase, transfer in, or point NS records to start as you get use of a single free working domain.
With your own purchased domain name, you can create and use subdomains up to the limit of the hosting service.
There is no refund for successfully completed domain orders. This includes for new domains, and transfer in, which extends expiry.
Hosting services (including DNS) and domain names are separate services. Cancelling one does not cancel the other.
Each hosting service uses a free DNS domain name that Hostfurl calls your admin domain. Currently these free admin domains are sub domains of adatempdomain.com and seasiaoceania.com. One is chosen at hosting service creation. It is not recommended they are used for any purposes other than for admin with Hostfurl and for testing.
You can host any domain name with Hostfurl without purchasing that domain name through Hostfurl (acting as your registrar), or without transferring a domain to Hostfurl, simply by pointing the domain's three NS records to 'custom nameservers' ns1.hostfurl.com, ns2.hostfurl.com and ns3.hostfurl.com.
Another easier option is to purchase a domain through Hostfurl. Currently .com, .club, .net and .org domains can be pruchased through Hostfurl.
With Hostfurl optionally acting as your registrar:
Hostfurl will put all domain orders on delay. One reason is to give you an opportunity to cancel the order without payment as once the order is successfully delivered, Hostfurl will have paid an upstream provider on your behalf. Hostfurl cannot obtain a refund and so cannot issue a refund or arrange for the funds to be used for anything else. You can set up sub-servers in advance. You can get immediate full use of sub-servers with new domain names by purchasing domain name independently and pointing three NS records as above. Some registrars allow refunds.
A fourth NS record, also used for the SOA record, is easily discoverable, but SHOULD NOT be entered to avoid service interruptions.
Whether using Hostfurl as your acting registrar or not, you get:
If you use Hostfurl for web hosting as well as for mail hosting you also get easy and free TLS/SSL certificate set up with Lets Encrypt