How do you get the rewards. Do you have to find all the shematics and do the levels on different difficuties or something

You will get the rewards when you have finished each stage. You can get 4 rewards on every stage.
1] Kill a certain number of enemies (disables).
2] Finish the stage in a certain time.
3] Do the Bond moment (if you press the Start-button while playing it will appear at the bottom, right under the missions.
4] Finish the stage in the 00 Agent-difficulty.
There's a total of 72 rewards, and with them you can unlock bonus-stages at 10, 25, 40 and 60 rewards. You don't need to do it all during one play-through, you can finish stage 1 with doing nothing and do all the rest during 10 other playthroughs.
Hope that helped,
Solid Bond