Are there any unlockables in Assassin’s Creed Revelations from playing the prior games

This one is pretty easy once you know what to look for. As you enter the castle, on the right, you can actually climb up to the outer wall. There are only two guards up here, so they should be very easy to take out. If you continue to follow the path, it'll take you directly above the prisoners, at which point you can easily do an air assassination on your target.

By taking over a city, you're effectively creating another source of income and supplies. Just like when you take over Templar Dens and renovate the stores in the zone. The difference here is that you acquire the different revenue/item generating sources through the different missions.

Once you have removed the templar influence in the city, you should send assassins to the missions that show the difficulty bar as stars (rather than diamonds). Being successful in that mission will increase the assassin influence in the city as well as other perks such as additional income, experience for the assassins that are occupying the city, crafting items and an additional slot for occupation.