Create CertificateRequest with .NET6

Question

I'm trying to create a CSR with .NET 6. I'm unable to test my solution so I have a few questions. But first of all, here is my code:

public string Create(Guid versionIndependentId, Guid networkId, string requesterName)
{
   int keySizeInBits = 4096;

   using RSA rsa = RSA.Create(keySizeInBits);

   string distinguishedName = GetDistinguishedName(versionIndependentId, networkId, requesterName);

   var certificateRequest = new CertificateRequest(
      new X500DistinguishedName(distinguishedName),
      rsa,
      HashAlgorithmName.SHA256,
      RSASignaturePadding.Pkcs1
   );

   return GetCertificate(certificateRequest);
}

private string GetCertificate(CertificateRequest certificateRequest)
{
   CreateCertificateExtensions(certificateRequest);

   byte[] encodedCsr = certificateRequest.CreateSigningRequest();

   return GetCsrAsBase64String(encodedCsr);
}

private void CreateCertificateExtensions(CertificateRequest certificateRequest)
{
   string dnsName = "example.com";

   string subjectPublicKeyInfo = "1.2.840.113549.1.1.1";
   string signatureAlgorythm = "1.2.840.113549.1.1.11";

   var subjectAlternativeNameBuilder = new SubjectAlternativeNameBuilder();

   subjectAlternativeNameBuilder.AddDnsName(dnsName);

   var nameCertificateExtension = subjectAlternativeNameBuilder.Build();

   var basicConstraintsExtension = new X509BasicConstraintsExtension(false, false, 0, false);

   var oidCollection = new OidCollection
   {
      new Oid(subjectPublicKeyInfo),
      new Oid(signatureAlgorythm),
   };

   var enhancedKeyUsageExtension = new X509EnhancedKeyUsageExtension(oidCollection, false);

   certificateRequest.CertificateExtensions.Add(nameCertificateExtension);
   certificateRequest.CertificateExtensions.Add(basicConstraintsExtension);
   certificateRequest.CertificateExtensions.Add(enhancedKeyUsageExtension);
}

private string GetCsrAsBase64String(byte[] encodedCsr)
{
   var csrBody = new StringBuilder();

   csrBody.AppendLine("-----BEGIN CERTIFICATE REQUEST-----");
   csrBody.AppendLine(Convert.ToBase64String(encodedCsr));
   csrBody.AppendLine("-----END CERTIFICATE REQUEST-----");

   byte[] encodedCsrBody = ASCIIEncoding.ASCII.GetBytes(csrBody.ToString());

   return Convert.ToBase64String(encodedCsrBody);
}

So here are my questions:

1. How can I use my own private and public keys to this process?
2. I don't really understand the CreateCertificateExtensions method, I copied it from an answer by bartonjs: How to generate a response to a CSR in .NET Core (i.e. to write a CSR signing server)? Do I need that? :O
3. Is adding dnsName = "example.com" necessary?
4. Do I need to add manually the Begin and End Certificate Request strings to the body? The code int the GetCsrAsBase64String method is quite clumsy because of the conversions.

@bartonjs Please. :D