Yes, you can purchase SSL from any company you like. For purchasing SSL, CSR (Certificate Signing Request) is required.
Installation of SSL certificate requires SSL Private Key. If the CSR has been generated on the Gotka Technologies server then you don't need to provide the SSL Private Key but if the CSR has not been generated at Gotka Technologies server then you have to provide the SSL Private Key associated with the SSL certificate so that the SSL certificate can be installed.
SSL certificates require a dedicated IP in order to work correctly. You will need to purchase one from us if the domain name does not have one already.