I'm using Gazebo everyday on my i7 ultrabook; and at home, on i3-7100 desktop. They both have Nvidia GPUs. But fortunately, Gazebo doesn't depend on the GPU. It mostly works on the CPU side. Most Gazebo plugins are built for CPU by default, AFAIK there is only GPU plugin for laser sensor, for 7.0. But I suggest using GPU for better desktop experience while Gazebo is handling your simulation on your powerful CPU.
So answer to your question is;
- RAM usage depends on your environment; gazebo plugins that you use/write, world file, also models and their amounts and details.
- It works with Intel HD Graphics. Tried lots of times. But also depends on your environment, and your CPU.
You just need an average processor to run it, and a processor that is above the average can give you a better performance. I'm running PX4 flight simulator with Gazebo on my;
- i3-7100 desktop (3.90 GHz, 2 cores, 4 threads, GTX1060) and Real Time Factor is mostly about 0.97
- But on my i7-4710MQ laptop (2.50 GHz, 4 cores, 8 threads, GTX960M), R.T.F. is mostly about 0.70, rarely goes crazy, down to 0.45 or something.
- Multi-monitor with Intel HD (for example my Intel® HD Graphics 4600 on i7) is already bad and almost impossible to simulate stuff. But on single laptop monitor, gazebo works normal with Intel HD graphics but don't expect it to work well if your processor is also old.
On multi-monitor setup, with GPU accelerated environment, gazebo works better.