I know that these questions are stupid but I need an answer to start my job, also a short answer
I wouldn't qualify the question as stupid There is no stupid question. But I would qualify it as incomplete.
What does "support for mobile" means for you ? There is no special service for mobile support. It doesn't mean you can't create a mobile portal with GateIn, but that's not something I've seen done so far.
For the second question, it's tricky, it will vary a lot on how you customize your portal.