Can I download someone's entire Mods folder and get all their custom content in one go?

It should technically work fine, with the benefit that the Resource.cfg will have already been made to suit the folder structure. However if it also contains mods that change the game behaviour, then you need to know what they are and how to check when they need updating. At the end of the day you bought the game to have fun with and if you'd find it more fun and less hassle to use someone else's mods folder then go for it. :)