Default language on envato is English so you will almost certainly not find anything written in Portuguese.
Magneto is not traditionally a blogging platform so while there are some themes with extensions already in place https://themeforest.net/search/magento%20blog this will drastically limit your search.
Of course you can try applying a blog extension to any theme but you would want to check with the author as to how/if it would work. You could even create a stand alone blog using a more focussed route like WordPress and just place it i a sub domain of the Magento site.
As for multi vendor sites - I’ve never seen this on Magento here. Again the extension probably exists but you will need some quote serious customisation help to install and set it all up. Also this may alter the license you need.
I don’t know how techy you are but if you plan to include all of these features I would strongly suggest looking at finding a freelancer (www.studio.envato.com) or even ask a magneto author on here to help find the right solution and set it all up.
It’s very unlikely you will find an out of the box solution (esp the Portuguese part) and Magento can be quite tricky to manage if you are not familiar with it all.
FYI your life would be much much easier on all requirement if you could use A WordPress commerce solution if that is an option.