You can download your images achieve here: https://www.midjourney.com/app/
Megapixel to Image Resolution Calculator: https://www.pointsinfocus.com/tools/megapixels-to-image-resolution-calculator/
Upscaler I use https://www.topazlabs.com/gigapixel-ai
Content inspiration: https://stock.adobe.com/pages/artisthub/
Photo and illustration requirements https://helpx.adobe.com/stock/contributor/help/photography-illustrations.html
Don’t forget to include a model release for an existing human and property release for a non-existent human (more about it in my next tutorial)