It would be better to say 'all systems go'.

It’s odd-sounding and you shouldn’t say it at all. Saying that something is a go or that a certain number of things are a go is ok, though not too strong, in my opinion. Saying ‘everything is a go’ doesn’t really make sense. Being ‘a go’ refers to specific things that you’ve planned. The trip’s a go. Hiking the Camino in June and then the GR20 in August are both a go. Everything is going according to plan. Both plans are still a go. Both plans are still on. I’m still planning to carry out all of my projects.

Keith has given you another saying that has the same meaning, but I think you might have been asking for a definition. It means there don't seem to be any problems, so we're going to do what we had planned to do.

We're good to go.