You certainly can use loops in different keys. It's actually ideal to in my opinion to create different feeling and tension.
A (somewhat) simple way to traverse into other keys is to learn the relative Major/minor keys. It's really quite simple and easy to figure out, they are a 3rd (up for minor-Major, down for Major-minor) apart from one another.
Beyond that, there is of course the minor harmonic and melodic scale, which is the same for any key so it's really not that intimidating once you understand the patterns. That can be useful in crossing over into other keys as well.
*none of these suggestions are requirements. By all means, you should experiment and do what sounds good to you, but the rules for music are so logical that they make the whole process a whole lot easier. Not much in life is as consistent and reliable.