Can I multiple run npm installs simultaneously

You can install multiple packages with a single command like this:

npm install --save package1 package2 package3 ...

EDIT:Installing packages separately, while theoretically possible, could create problems. When an install command is issued, npm looks up existing modules and downloads missing packages into a staging folder .staging inside node_modules. Once downloaded it copies the packages into the node_modules sub-folder (and removes .staging).

In npm2, modules had their own dependencies stored underneath themselves like this:

node_modules  - dependencyA    - node_modules      - dependencyC  - dependencyB    - node_modules      - dependencyC

Notice how dependency A and B both rely on C. If C is the same version in both cases, it would use twice the space.

In npm3, dependencies are flattened like this:

node_modules  - dependencyA  - dependencyB  - dependencyC

If for some reason an older version is used in a dependency, it follows the npm2 convention for that module.

I'd stick with the intended use of npm and use the multiple install functionality.