Yes, you can ride an alum bike. Most Alum bikes have a rated tolerance to handle 300lbs of rider and gear. Reality is they can handle much more.
I used to be over 360 pounds with some gear. I had no problem with my Crosstrails frame. Now the wheels on the other hand......
I would suggest riding with the current wheels and if they break or continue breaking spokes, then to worry about getting a new better set.
Steel is nice, but it's not going to be any better or worse than aluminum for a new rider.