You're probably better served by filing to be treated as a S- corp. for Federal tax purposes; this way you you avoid self employment taxes. It's a bit more paperwork, but given his occupation, you will probably pay lower taxes to boot.
Also, if the IRS has not said you need to pay quarterly payments, don't. As long as you don't owe over $400 in taxes at year's end, you will not need to pay quarterly. Thus, you have the money which can earn interest, and in December, run a mock return and figure out what you need to pay by Jan 15 of the following year to stay within the $400 rule.
