That sounds like a good strategy anyway, Chaosti. Maximum respect for going for Impossible for your first game. Griffins are great for retaliation, especially if you get the -30% leadership banner. Sounds like you are going fine.
I was annoyed at myself for using up the 13 Horsemen, as I wanted to Sacrifice something to get a full stack of them, and then I realised that I had parked 4 of them in King Mark's castle! So now I have 33/33

I love Horsemen. They are up there with Griffins as the best melee units.
I forgot to mention before that I found a lame exploit in Freedom Isles. This is related to the Bob Devis quest, for which you get the pirate halberd and some cash. I don't like the halberd but it's worth 20,000 gold if you have Trade 3, so I usually take that and give Devis the money. But I discovered today that you can get the halberd, sell it around the corner in the castle, then go back to Bob and tell him you'll keep the money (i.e. give him the halberd) and I get 'quest completed.' Lame or what?