For #1, Shared memory is memory (potentially) used by more than one process. This is basically if you run the same binary file in multiple processes or different processes are using a shared library. The heap is where allocated memory is stored (when you use new in Java). Since Java has its VM, it is allocating a lot of memory on the process level that you don't see in your java code. I think that yes, the majority of that 135 MB is from the JVM code/data itself. However, there is also the memory taken up by the stack (when you make a function call and have local variables) as well.
For #2, different amount of RAM would not affect how much "memory" is used when we let memory equal RAM + swap space. However, different processors (especially if we're talking about 32-bit vs. 64-bit) may use different amount of memory. Also, the way a process is compiled may change the amount of memory used because you can instruct a compiler to optimize for memory footprint over speed, as well as disabling some or all optimization altogether.