The boiler should have an auto vent so will be self bleeding. If you hear gurgling noises it is usually air trapped in the pipe work at bends where the flow is downwards. Normally over a period of time it ends up in a radiator where it can be bled off.
You should always add rust inhibitor to modern heating systems to help protect the boiler heat exchanger.
Normally you add it into an empty radiator before filling the system. You can buy injection kits, but they do cost more.
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