I am in a situation where I own BTC on the same address as BCH and I would like to exchange BCH for BTC.
1) My plan is to move my BTC to another address before moving my BCH to exchange service. am I right to do so?
Why will you move your Bitcoins if you only want to convert your Bitcoin Cash to Bitcoin? just move your Bitcoin Cash to a trusted crypto exchange that supports BCH and convert it to Bitcoins.
2) I don't know if I can move my BTC to another address as some people say the Bitcoin gold hard fork has already taken place. So I assume there is a risk to loose my Bitcoin gold doing this?
You can move it anytime before the hard fork. but you have to store it on Bitcoin wallet which you hold the private key or put it on exchanges that support Bitcoin Gold before the hard fork if you want to receive your BTG.
3) is there a script like coinb.in to create and broadcast BCH transaction?
I don't know, I don't use coinb.in or any scripts.
4) is there a risk loosing my Bitcoin Gold by moving my BTC or my BCH right now as some says Bitcoin Gold hard Fork has already taken place?
There is no risk if you will transact your Bitcoins before the hard fork but there is a risk of loosing your coins if you do it during the hard fork and also don't transact for a few days until they officially confirmed that the fork is successfully done.