The topic of Blitz vs Souveran has been covered a few times here on this forum. I'm sure a search will yield some good threads on the topic. But to sum up, Blitz has better durability, but Souveran may provide a slightly better shine, is an extremely easy wax to use and doesn't stain trim. The downside to Souveran is the durability (which isn't ALL that bad) and the price (which I don't think is all that bad either)
Before you apply Souveran/Blitz for the first time, prep the paint to remove all surface contaminants and imperfections. Whether or not OHG is part of your surface prep plan is up to you. Then top everything off with a coat of Souveran/Blitz. Thereafter, you would use IHG followed by Blitz/Souveran as regular ongoing maintenance for your car.
I've used OGSO over Souveran before and it works fine. I've also used Pinnacle Crystal Mist, E1 Wipe and Shine and they all work fine as well. Any QD containing carnauba would probably be your best choice (OGSO, Crystal Mist, Clear Pearl).