Hi Francesco, Being up for something or being down to do something are both equal informal expressions. I would say the second way is more slanglish than the first one. You could say: Let's meet up this weekend to practice English. Are you up for it ? Or Are you down to do this ?

You cannot say it with down. Use up instead! 'You're up for meeting this weekend?' Or omit the be verb (are) if you're having a very informal conversation. Now, you cannot say, 'up to meet...' Because it sounds very weird, has a very formal tone to it although you would never use sentences like these in the first place while making a formal conversation.