I'm guessing you're talking about Disney World, because most people don't stay at Disneyland for a full week. Have you been before? What time of year? How crowded it seems will depend on how crowded it was when you went before. Evenif you don't care about closing times, you can look at Disney's posted closing times to get a good idea of how crowded they expect the parks to be; the longer they're open, the bigger the expected crowds (and the more staff they'll have on hand). The last week in May is less crowded than the first week of June, and a LOT less crowded than the middle of June, but it's a lot more crowded than, say, January or September.
It also might help to consult messagplanning sites (like allears.net), message boards (disboards.com) or a virtual concierge company (like tourguidemike.com or touringplans.com - both are excellent) to help you determine which parks are most crowded on which days. For instance, I know the annual Star Wars Weekends will be going on in May at Hollywood Studios, so you'll want to go there on a weekday for sure, unless it's important to you to see the Star Wars characters.
The cast members are pretty good about confining smokers to certain areas in each park (I've run across people who are smoking in the wrong areas, but not often, and we go a lot). As for the perfume, there's just no way to forecast or prevent that, unfortunately.
Definitely request the Guide for Guests with Disabilities, as someone else suggested. It should give you lots of tips. There are certain rides whose queues will allow you to skip ahead of the line, but many of Disney's ride queues have been redesigned so that wheelchair guests wait with everyone else (this was done to prevent people from renting wheelchairs for the day just to skip to the front of each line). If your husband's intolerance to smoking or perfume is something that his doctor would be willing to document as a reason he should be given special access, you can bring that with you and turn it in at guest services for a special pass. They're not easy to get, but usually with medical documentation it's not a problem.
Good luck, and have a great time! Disney World is my very favorite place to be!