If you want a free engine that has a huge community behind it I would suggest Ogre. It's got a TONE of possibilities to practice your techniques with but sadly can't handle modern content and caps out at about 20,000 pollys on screen. But it works great for particles, 3D rendering, Post processes and has great documentation and a dedicated community that will answer your posts in as few as a a couple hours.
Or if you want a little bit more Modern stuff I would suggest either Game Studio Express through microsoft or Torque/TorqueX(XBox 360 counterpart) There done in C# but it's a good language to learn and is not a lot different from C++ or even Java. Kinda bridged the gap for my team.Game studio Express is in beta so it's redistribution is not finished and adds about 100mb to your finall project size because you have to ship all the XNA framework as well as Game studio Express and Visual C# updates this is in the fixings though. Also no particles and sometimes it messes up model imports.
Since you want to be a level designer and programmer I would suggest Torque since it has a lot of scripting and more of a Gui feel to it. Also it's more geared toward 2D games but can easily support 3D games aswell
Hope this helps.