Initially, as it sounds like you have very few employees right now, you may want to look at how much time you need to get your product out the door, then double that, and determine how much of a problem that would be if people are heading off to vacation.
You will want to look for people that are as excited about your idea as you are, as you need people willing to dedicate themselves, as your core group, so you may want to look at offering some equity, after a vesting period.
The reason being, that, though you may offer vacation time, I would suggest that it be paid time off, so that people can have their vacation and sick time, as you don't want to limit how often they can be with a sick child, and initially 3 wks may be enough, assuming that is at least the legal minimum, with the understanding, perhaps in the contract, that after 1 or 2 years that it will increase.
If they are forgoing their vacations to work long hours to help you, you may want to let them know that when the product is launched and money is coming in that you will do something for their sacrifice. One company I knew of would spend all of the money they made over what they predicted on something like a cruise for all their employees and families.