I'm not a fan of carbon forks, but there's solid data that all-carbon forks are stronger and less pone to failure than carbon forks with steer steerers. Carbon forks have been around decently long enough and have established a reasonable safety record. So if you're buying a carbon fork, you might as well go all carbon.

Without seeing it, it's impossible to judge the cause or seriousness of the groove in the steerer. It's probably from rubbing against the ID of the lower cup, but that's a mystery you should try to solve before going farther. As for the expansion plug, next time around consider mixing some abrasive with paint or nail polish and applying a band around the expander. This will give it some bite, and prevent slippage without the need to over tighten.