While the motivations a laudable I worry about this project. There is no way you can determine if the radiation level is safe with equipment like this and you might lead people into a false sense of security or insecurity.
The tutorial link you posted makes no mention of dead time or dead time correction and while you might get some beta and gammer readings the most ionising alpha radiation is virtually impossible to detect with that tube.
The most dangerous problem is the ingestion of small amounts of alpha emitters, there is no way you are going to detect that. I would rather people relied on official measures than simple systems like this.