First, if your husband has physical issues, then I'd avoid going back into a field where his condition might jeopordize his livelihood. Since IT skills don't really require much in the way of physical skills, and since he's got some experience & interest in IT--and (especially important) there's a plentiful market for IT skills--IT seems like a solid choice.
Next, like you alluded to, he'll want to narrow down his niche so that he can specialize. NOT specializing is a common beginner mistake, and it leads to struggling for business, charging a low rate, and competing with tons more people. Instead, if you focus on a specialized niche, you'll be able to:
-->charge a higher rate (and therefore work less),
-->have less competition, and
-->be easier to find by potential clients.
For example, in my niche, there are probably less than 3,000 potential customers, and literally a handful of competitors. Given that the clients are extremely profitable (law firms), that means that I'm able to charge a high bill rate, which, in turn, means that I can work less to make the same amount as someone with a lower bill rate. Of course, this assumes that you have specialized knowledge & experience--which provides a barrier to entry for your niche (good for you, since that means less competition).
Don't worry about needing a degree in IT. I don't have an IT degree and I have no IT certifications, and my bill rate is $150-$175/hour and I've been fully self-employed making over 6 figures for the past 4+ years, steadily growing my business during the economic meltdown.
And don't think that you can't do SEO just because of what others say--even if they have some experience. I know lots of people doing SEO who starting doing it in the past couple years.
In short, there will always be naysayers, but what's important is to do data-based instead of anecdotal research to see if your idea will pan out. Google Adwords (https://adwords.google.com) and other tools provide great market data and can even give you an indication of how profitable a market is (based on how much specific keywords cost). Use that real-world data to inform your decisions.
Speaking of anecdotal evidence, one trend that appears consistent over the past few years is that local businesses need help with online marketing, since they don't know and aren't inclined to learn how. As a result, learning how to market local businesses using social media, SEO, SEM, establishing a web presence (by the way, it's SUPER easy and cheap to build a website using WordPress), using social marketing tools like Groupon & LivingSocial, etc.
Anywho, if you want to start consulting, you can check out an interview I recently did where I talk about how I made the switch from employee to consultant, and where I give actual income & rate numbers: