PRSI is payable after his business expenses ( including any wages ) but not after health expenses or pension payments. Health Levy goes the same, after business expenses but before health expenses/pension payments.
On the employee front :-
1) If you have children you will be getting the Home Carer Credit if you have no other income. You would lose that if you earned over the cut-off amount for it ( circa €5,000 )
2) To be an employee you must
(a) be registered and have a tax credit cert allocated to you for your employment with him
(b) be actually working for him
(c) be actually paid
You are not insurable working for a spouse so PRSI is not payable by him for you and you would not qualify for jobseekers benefit or disability benefit as a result solely of this employment.
The advantages of employing and paying a spouse who works for you are the increased standard rate cut-off point so if he was earning sufficient to be paying higher rate tax then your earnings would be taxed ( to a point ) at 20% and he saves at 41%+PRSI+Levies. If he is taxed only at 20% then the savings are more marginal.
Payment can be a moot point in relation to spouse employments. If he presently draws say €400 pw for housekeeping then he may determine to draw €200 for housekeeping and €200 for your wages. If you then choose to apply that €200 into the household pot then that's up to you. The issue is there must be genuine work carried out and be seen to be paid for.
It can also sometimes happen that the spouse doing the work operates as a self-emplyed person themselves. This is fine if they are doing similar work for other persons, e.g. a bookkeeper with their husband and others as clients. However if they are working only for their spouse the issue of the status of being self-employed -v- employee comes into play and you may be judged to be an employee anyway, not self-employed.