Minecraft – How big is the world in Minecraft Pocket Edition

For the textures, you can easily change it by changing the terrain.png file with your desired texture pack. But beware that PC's terrain.png may vary with PE's. Try searching for a similar or exact texture on the Minecraft Forums. They have lots of ported texture pack.

For maps, you will need to first port it because MCPE maps aren't infinite and a portion of the world will need to be cut, pasted and then saved in MCPE format. Then you can transfer it to your Android device.

Note: My previous answer was for iOS devices. I have changed my answer to fit the question and hope it helps.

Pocket Edition does not even have a login system required to play the game.

The Realms Alpha login under the options menu, however, is the same as on your computer, provided you login to Minecraft on the PC with a Mojang account (login with your email address).