Completely safe to use. Doesn't get you banned or anything. As it says though it's recommended to not use the program while playing a game on a VAC server cause it could result in a ban due to it thinking it's a cheating program but yes, it's 100% safe

The program doesn't get you free stuff really, it just idles games you've bought/played and gets cards you're available for.

Up to 30. It's best to keep it at one at a time though. More drops that way

I don't know if this will help anyone but I noticed from just my own personal experience that when it did only 1 game at a time it obtained them quickly, though I left it on all night and it started doing 8 at a time... Obtaining no cards. The next night I switched it to do only one game at a time, came back to more than 20 cards. I think steam is able to pick up that you're using this if it runs more than one game at once. If you change the settings to do only one game at a time it usually obtains the cards a lot faster.

This is all just from my own experience with it though. Not sure if it'll work for everyone but it deffo did for me