Some basic newbie questions

Here for the first time, and just seeking some basic answers if folks don’t mind:

1.) Can you just submit as many designs as you want to the marketplace? As often as you want?

2.) Is there any specific guidelines as to what category you assign a design to? For instance, if I submit a design to the marketplace that’s relatively simple, or just a phrase/slogan, can I just select to sell it as everything relevant (IE, All t-shirts, hoodies, sweats, masks, etc) or are there limits?

3.) Do you accrue any billing or fees per usage, or is the best way to use the site/marketplace without your own store just to add as many catchy and/or quality designs as possible to hope one of them catches on and becomes a bestseller.

4.) Any specific methods and/or tips for having your designs featured towards the front of the marketplace catalogue and not buried on page 160 or something?

Thanks in advance.