Even if you're not an expert at all of these things, if you know what they're for and can read the documentation and make all of them work in an afternoon, then you're well-equipped (better equipped than many Microsoft "certified" techs) for the job. Most small businesses don't even know what they need, much less how to set it all up. So, when you go in, you'll find that they have no idea what you're doing, why you're doing it, or how it all fits together. How you explain it is more important than how you implement it when it comes to whether you're called back or recommended to other businesses. It has to work, of course, but as long as you're explaining the job clearly and in simple terms, the customer will remain happy (try to look busy, as well...sometimes you'll be waiting for installs and such...do something else during that time, even if it's busy work).
Note that I'm not necessarily recommending this path. IT support sucks. It's a very stressful field, where the only time you hear from people is when there's a problem. In fact, the only time you hear from people is when there is a problem so severe that they can't get work done (people are so afraid of computers, and of thinking about technology, that they'll ignore trouble signs until the breakage is complete). Thus, your customers are almost always stressed out. I frequently worked for a company that had a quarter million in daily revenues, and so a day with all of their people off-line cost them significant sums of money. I have great respect for the fellow who built and owned the place, as he kept his cool like a champ, no matter how tight the downtime schedules were...but some of his employees (and share holders) did not.
Oh, yeah, you'll also work a lot of nights and weekends, because that's when companies can afford to be completely off-line.
Serious Linux nerds are in high demand and low availability almost everywhere I've ever lived. But, if you're not well-equipped for IT, that might not be the way to go. Tech support is also the highest stress technical career (there was a study about it a couple of years ago, and if I weren't lazy I'd look it up), so you don't want to do it for long if you haven't the patience of Job. But billing $100/hour is not at all difficult, so you only have to work three or four days a month to scrape by...don't underestimate the time spent on paperwork and such, though...some companies make you work an extra day for every couple of days you work, in dealing with expense forms and other assorted crap. I much preferred working for small companies, where one person made the decisions and when he or she said to the accountant, "Write Joe a check", it would be in my hand before I walked out the door.
But, IT has the advantage that you're generally working on small jobs--things that can be fixed in a few days, or a couple of weeks, tops. They are well-defined, like, "We need to move our web servers to a new data center", or "our mail server isn't filtering spam and it's letting viruses through". You know when you're done with this kind of project, generally.
That said, startups are kinda like a marriage. Having a little something on the side isn't likely to turn out good for the startup. Have you considered raising a little money to get you to launch and revenues?