If I recall correctly I managed to get enough readiness even in vanilla ME3 without playing multiplayer - but I REALLY had to do every single one of side quests correctly :)

You are incorrect, you can use Microsofts License transfer (support.xbox.com/en-US/xbox-live/marketplace-and-purchasing‌​/…) where your downloadable content rekeys for new console, so the drive can be swapped without problem.

If you hide your helm graphics it won't show to other people.

I tried that, but the mage just teleports away and throws the spell on my party killing them... His spell seems to be instant cast (the vortex is thrown down in a second right at the start of the battle, stunning my party).