Freezing Soup Made Partly from Tins
There's really nothing to worry about. As long as it's safe when it goes into the freezer, and it's in a reasonably-sized container so it doesn't take forever to freeze, it's going to be safe when it comes out. Freezer storage limits are more about quality than safety; things can dry out or pick up odd flavors, especially if they're not well-sealed, but it'll be safe indefinitely.

I'm guessing you want to freeze it in reasonable serving sizes anyway, so you shouldn't have problems with container size.

You can do the cooking before freezing, or after as part of thawing, whichever works better for you. I'm guessing that cooking after would save a bit of time, and it also means it'll go into the freezer a bit cooler and freeze a little faster. But cooking before is totally fine too. All that really matters is that it doesn't spend more than a couple hours total in the danger zone (40-140F/4-60C), and you can accomplish that either way.