The Android build instructions answer most of your questions for you:
You need at least 30GB free disk space for a single Android build, and more than 100GB for a full set of builds.
You need at least 16GB RAM.
You must have a 64-bit CPU.
In addition, I would suggest at least a quad-core system.
Beyond those base requirements, the question you need to answer is, "how fast do I want this build to run?" The faster you want it, the more strain you will put on the hardware, whether that is real or virtual. For example, if the build produces 30GB of output and you want the build to complete in 10 minutes, your disk had better be able to sustain 30GB/10m = 51MB/s transfer rates or better. Likewise, if the build, with Accelerator, generates 10GB of network traffic, your network had better be able to sustain 10GB/10m = 17MB/s transfer rates. You can get some information about disk and network utilization from emake's performance metrics, generated by adding
--emake-debug=g to the command-line. Then you can look for the
Bandwidth metrics, for example:
Network to agent: 11386.6 MB, 3.6 MB/s active, 9.1 MB/s overall
Network from agent: 16843.8 MB, 15.5 MB/s active, 13.4 MB/s overall
To disk: 26852.5 MB, 40.7 MB/s active, 21.4 MB/s overall
From disk: 15565.5 MB, 4.9 MB/s active, 12.4 MB/s overall
So, look at the characteristics of your build, consider what your performance targets are, do the math and check whether your proposed system is capable of delivering the performance you desire.