Depending on your Shopify plan you need to watch out for the 50,000 product upload limit, excepting Shopify Plus. If you try to load all products from all brands with the app, you will run into this limit and find that the upload speed slows down considerably after the first 50,000. You can continue to load products, but at a rate of only 1,000 new ones per day.
You have 3 options with this scenario:
1. Wait patiently for the rest of the products to load 1000 at a time.
2. Upgrade to Shopify plus plan which has unlimited upload, but is a bit costly.
3. Add more filters to narrow down the amount of products flowing into the store.
Keep "Import products with zero stock" and "Allow products without images" unchecked, but consider check marking "Exclude universal fitment parts". Any of these will exclude a lot of products you maybe won't want in your store anyhow!