Hello.
1. No. A letter should suffice.
http://www.immigration.govt.nz/opsmanual/41495.htm That said, some COs have an automatic reaction - 'Where is your IELTS?' - when faced with an application without one, so it is advisable to mention in your cover letter that you are sending a different form of proof, and normally, a reply reminding them does the trick. Bear in mind that a CO has the right to ask for IELTS after all, as mentioned at the link, in case of doubt.
2. Yes, you have to have your qualification assessed. INZ will be going by the current list, not a previous version. Notice, this list does not go by a degree, and an institution, separately - the courses have been checked as that-degree-from-that-institution, and the dates mentioned are also specific and have to be taken into account.
3. If you need the points from your husband's qualification, you need to be sure that it is either exempted, or assessed. Again, as mentioned for answer 2 just above, be sure it's the degree he has, from the institution that awarded it, within the dates given on the exempt list. If his bachelor degree is enough to get you the points, you don't have to bother with the MCA.