1) The cobra MKiv is available to all players who own the
core game before the horizons release. Frontier said its their thank you for joining in the first year. Im not sure if you have to order horizons or not. Someone please correct me if im wrong, but i dont think you have to own horizons to get the cobra mkiv. Just own the core game before the horizons release. So if you don't own the game yet, and have horizons pre ordered, you won't get the cobra.
**EDIT**
found the source,
https://community.elitedangerous.com/node/247
Elite Dangerous: Horizons will be available to pre-order on our store today, and I’m very happy to announce all existing Elite Dangerous players will receive a £10 loyalty discount off the Horizons retail price. Existing players will also unlock the exclusive Cobra Mk IV ship in Elite Dangerous: Horizons. The Cobra Mk IV will be available in the game only to players who joined us in the first year – forever. It’s our ‘thank you’ for your faith in the game, and you’ll see more of the Cobra Mk IV in Friday’s Peek Of The Week.
2) No, at least not in the sense i think your asking. The 1.5 ships update and Horizons will release at the same time. As 1.5 is not available right now, you cant get the ships yet. HOWEVER, since the ships are available in horizons, and horizons is in beta, the 1.5 ships are in the current beta and you can fly them right now. Just remember, non of you beta progress carries over to the main game.