Basically you got it right, but there are few clarifications/corrections to be made.
First of all not all Creative Commons licenses are equal, some of them are non-commercial usage only, some of them are share alike and most of them requires attribution. So that's important thing to keep in mind when searching for Creative Commons licensed textures.
Another thing is specifically about Textures.com textures usage. Actually you are allowed to use their textures for your models and sell those models. Resseling textures, or pack of textures is forbiden of course. There are few additionals requirements and exceptions, so make sure to read full license on the site: https://www.textures.com/faq-license.html#anchor-3dmodel
Every other texture site has their own license, so you need to read them in order to know what's allowed and what's not.
And last thing about CC0 or public domain textures. You can modify/remix them and sell as standalone textures, but modifications needs to be substantial enough for it to be considered different texture. Reselling unmodified textures is not allowed.