OK......
You're gonna play Hold 'Em right? Will it be No Limit, like on TV, or what is called a "structured" game, i.e. limits on the betting?
You're much better off with a structured game, since the players money will last longer.
If you play no limit, the whole evening could theoretically last only one hand.
Also, if six people are gonna bring $40 each ($240), and you want to take $60 for expenses and make a $60 profit, you'll be taking half the money at the table. Conceivably, at the end of the night, there will be no winners - everyone will have lost something. In fact, taking 50% of the money makes that almost a certainty, even if some of the players buy more chips.
Even if you were just taking out enough to cover your $60 in expenses, that's still a rather a high percentage of the total amount at the table to be removing from the game.
If you want this to become a regular game in which the players have fun and you make a profit, there have to be winners as well as losers.
Also, I'm not comfortable with your idea of having everyone buy-in for $40 and only giving them $30 in chips.
A steady rake of 10% of each pot like they do in the casinos. is a much better way to do it, because psychologically the players don't feel it (after all, after you've just won a pot you don't really care that 10% of it is missing) and also, the winners wind up paying more than the losers.
The danger, though, is that one pleyer goes on a hot streak early and cleans out everyone else long before you have the chance to get back your $60 in expenses, so you have to make sure that the stakes are low enough to ensure that the game lasts long enough.
With a $40 buy-in, you're gonna need to keep the betting levels at about 25 & 50 cents, believe it or not. Those stakes may be too low to keep everyone interested.
To reach your goals here, you need everyone to buy in for at least $80-100 or so, and then maybe have betting levels of $1-2.
To answer one of your earlier questions, BTW, the game ends when either everyone runs out of money except for one person, or at a certain time which you would pre-determine.
Then you cash in everyone's chips and they go home.