Ran 20 routers in GNS3 on macbook air mid 2013.
This test is not about the testing of topology or specs, I simply place the 20 routers if macbook air could ran them.
Here is specs.
Since my first language is Japanese, my OS is running with Japanese languages. But, I am sure you would guess what it says below.
Memory is 4GB, SSD is 256GB, model is macbook air mid 2013.
This system run with core i5 cpu and clock speed is 1.3GHz. If the CPU is generation of core2duo, they would only run 10 routers are maximum.
After idle PC, the usage of CPU is below.
At this time, I did not do the "idle max=100", so the usage is a bit higher. If I spend more time to tune those usage things, it would go under 10% or around.
One point, I bought a 11 inch Macbook air mid 2013.
This model is best computer to bring around, but is a bit too low resolution to build a topology which include 10 or more routers. It depends on your use of computer, if you do not need to buy 11inch and you are willing to run GNS3 on macbook air 2013, I strongly recommend you to buy 13 inch model. Otherwise, you may use external display, resolution will not be a problem.
If macbook air 11 inch model gets a resolution of Full HD, it will be a greatest computer ever in the history.