You should choose all font weight variations that you use in your website content and vice versa do not choose what you don't use. I.e. if you don't have italic fonts then do not choose italic variations. The less font weights you use the less font size and as result website loads faster. Default Athlete font is Open Sans, font weights used: 400, 600, 700, 800.

There are font weight variations for each font option but you don't need to set it for each font option. Only for unique font name. I.e. if all of your fonts are Open Sans then you only need to set font weight variations once in any of the font weight options, because they will be merged anyway. But if you choose different font for some of the elements i.e.: Poppins for titles, then you need to choose font weights for this font.

Enter purchase code and click Save Config button above to register theme on current domain.

One purchase code per one Domain name.

After you registered domain you can deregister it and use same purchase code to register theme on another domain. To do this you need to remove purchase code from this field (leave it empty) and click Save Config button. You should do this before migrate to another domain name.