As I am experienced in cracking (well, I think I am based on my experience) I can always recommend you to buy
https://snipr.gg/, because for a long time this software established a big community and also has many configs with which you can start checking accounts at a lot of services. If you are experienced in what GET and POST Methods are and know how checkers work you could try to code one yourself, but trying to get hands-on
https://bullet.black/ would also be fine. And to the point of what VPN you should use: Always use a VPN that has a non-logging policy that they also follow. I always recommend using
https://perfect-privacy.com/, but to be honest, the best provider, in my opinion, is
https://securevpn.to/. I use them for a long time now, and they know what they are doing and how to stop data leaking from you to third-party services. They are a service for encrypted private internet access for almost five years now.