Albedo, can you tell me whether I can play MP without it affecting my SP campaign? I was watching my hubby try MP, and it showed his character under my account name (we play on our own machines with our own characters, but under one Origin account). As far as I know, it's not possible to delete anything done within MP. (I'm being nitpicky and going for my 'perfect' personal canon SP playthrough, and am a bit wary of having anything external affect it.)
I'm not actually sure, sorry. I finished my playthrough before I touched MP. Supposedly MP experience and character promotions increase your Galaxy at War rating making it more likely you'll get a good ending, but I don't think that sucking at MP will reduce it.