You’ll first need to make an account on Melee.gg. After that, you can go to the DreamHack home page to apply to host a Regional Championship Qualifier. Once DreamHack reviews and approves your application, you’ll receive an email from Melee.gg that you can return to the site to finalize purchasing of your RCQ Event Kit(s).
No. You will be using EventLink to schedule and run your Regional Championship Qualifier unless given permission by Wizards of the Coast to use other software solutions.