We played through with a friend that was starting fresh, just had them make their own world and came in naked on our existing characters. Once they reached a certain tier of armor and weapons we would just grab that same tier from the stash in our existing world or just crafted it in our existing world since we had abundant resources already farmed there. Put us pretty much on the same page as the new player, but saved from wasting resources on crafting 3 sets of gear and allowed them to upgrade their gear faster and kept us from polluting his play through by bringing in resources. Our existing characters were obviously stronger than their new character because of skill levels, but I don't think it is really that noticeable. Whats more noticeable is just the difference in skill from having played the game several hundred more hours than them, but there really isn't anything you can do about that besides handicapping yourself with lower quality gear. You can't really ever recreate the magic that was the first time playing through, so when someone new starts, all you can really do is try your best to not spoil it or carry them.