here are various changes between CMAQ v5.0.2 and v5.2.1, and in general we recommend the latest version. Version 5.3 is expected to be released in a few months.
But I thought your question was whether it is feasible to run CMAQ on a single PC. The answer to that question does not change significantly between CMAQ versions. For a mesoscale simulation, we typically use multiple cores in a parallel computing environment. I am not a hardware expert, but the computing resource you describe may be inadequate to get simulations completed in a reasonable time frame.
You might first try installing the model and running the benchmark test case on our Southeastern US modeling domain, and see if you can get that to run.