Should I Change My DNS Server?

Hi...

I'm using Contabo's VPS with Contabo DNS with single IP...

1st - Should I change hostname to my own domain hostname or instead using Contabo VPS Default hostname.
2nd - Should I change Contabo PTR record in Contabo's Customer Control Panel to my domain PTR? for example.. Contabo set PTR to wmi123.contabo.net - should i change it to sistem1.mydomain.com then set my hostname to sistem1.mydomain.com?
3rd - Is it OK if i just use contabo's DNS nameserver - and what should I set in CWP?
4th - Any effect to SSL if i use Contabo DNS Server?

Thanks in advanced...