Honestly, after reading your post I just want to see pictures of your army.
Not a bad selection of tanks (never come across a Carnodon, didn't realise they were playable in
40K). Your firepower is a bit short ranged but with the size of
40K tables today that might not be a bad thing.
I feel that you're going to have a hard time taking and holding objectives. Your limited number of Scions aren't going to help much in that regard.
Personally I would take more troops, though that goes against the theme of your army and I might just be saying that because I'm not a big fan of tanks, prefer my Imperial Guard in the infantry variety.