I have a surface so my storage space is very limited, would i be able to install UE on an sd card and it still run ok?
It can’t, it has some dependencies that require it to be installed on the machine. Also, if it could, it would run poorly due to the speed of reading SD cards. Also, if you’re talking about a regular Surface computer, then it doesn’t meet the minimum requirements to run UE4 anyway since it does not have a powerful enough GPU.