I miss the good old days when level design was all about placing large blocks (brushes) and slapping some textures on them. Things are a little trickier now a days there you need to be filling your environments with pre built models. I'd say jump in the deep end and get unreal engine 4. one month subscription is $19 then you can cancel and keep using the tools. You can make some amazing environments in it, then as you get more advanced you can spice it up with all manner of particle and lighting effects, then you add layers of interactivity with blueprints. However you'll probably want to learn some low poly modelling too so you can make your own assets.
level design is awesomely rewarding when you complete something and other people can explore the wolds you've created. Good luck