Importing Assets and Making Levels

Hello so I just started in the process of making a maze like game that will eventually be for an iOS app. What is typically the best way to make levels in Unity. As a test I was using a player sprite with 1000 x 1000 resolution .png file and then scaling that down in Unity by .1. Will there be an issue if I make the levels specifically in a program like photoshop and then import a huge .png file to use for each level? If so what are some better ways to create a level without having to use such large files in the game? Any advice would be helpful. Thanks!