I can't help with the support issue, however the line of filament is a purge line to make sure filament is flowing.

It is set with the start and end G-Code in the printer settings.
You can cut and paste the G-codes from your Ender 3 into your new printer start and end codes to replace what is in there.

Just copy and save any G-codes from the Cobra Max just in case.

Just as an aside, I have found the Prusa slicer gives me good results and is easier to use than Cura for me.