While you wait for your reseller's permit, you should not get in touch with suppliers yet, as you would want to have everything set up before reaching out. A lot of suppliers will not approve you if you do not have your resellers permit set up yet.
So for the time being, I would focus going through the course and making sure you have a good understanding of the business.
If you are already feeling confident and want to take action, then I would start at least putting together a list of suppliers. You do not need to get in touch with the suppliers yet, but at least have a list together. That way, when all your information comes through, you are ready to hit the ground running.
My amazon account is set up but not my business, what can I do?
What should I do while I wait for Corpadvantage?
What should I do while I wait for my resale certificate?