A fairly decent amount of my business is doing just what you describe. Let me pass along a couple of wrinkles to keep in mind when seeting yourself up.
1. Do not depend solely on plugins/cleaning apps as your tools; get plenty of practice using manual tricks and techniques with more conventional tools including - but not limited to - gates, EQ, dynamic expanders, reverbs, phase controllers and manual waveform editing. Practice not only to get good at the techniques, but - to keep your costs down - to get fast at them.
The reaoning behind this is that if you want to be successful at this, you have to not only do a better job than most automated cleaners can do because (as this board proves every day) anyone with a modem or a credit card can get the same NR packages as you have and do it themselves. You have to be able to show that you can do it better in order for them to be willing to hand over their wallet, and you have to be able to do it fast enough for you to be able to actually make money doing it (if you get get $20 for something that takes you 8 hours to do, you're making less than you would jerking sodas at McDonald's.)
Also, frankly, the automated tools just don't to a proessional job all by themselves. They may do a good enough job for some of your customers, but if you have a classic audiophile on the hook who wants you to restore and enhance his irreplacible vinyl collection, he is going to want and expect top-notch results.
2. Once you have the tools and techniques in place, *charge* for them. I mean, don't be afraid to tell folks your services are expensive. Of course your services have to be up to snuff first

, but as long as you can put your money where your mouth is, speak up loudly.
A few reasons for this are: you have to seperate ourself from every joker and his brother out there who has a cracked copy of the Waves Restoration Pack and thinks that's good enough to hang out a shingle. There are almost as many of them giving us a bad name as there are college students with Cakewalk and a Blowfish compressor plugin that call themselves inexpensive "mastering engineers."
Also, even when you get fast and good at it, quality restoration and enhancement takes time and talent. You need to get paid for it, otherwise it's just not worth the effort.
Finally, the real market is the aformentioned audiophile who has vinyl or tape collections that they want converted in whole or in part (usually in part at a time.) These collections usually include hard- or impossible-to-replace recordings and are in part or in total worth a lot of money and sentiment to them. They are not only goingto want a truely professional job, but are going to be willing (or easily convinced) to accept that a professional job is not something that can be done on the cheap.
As far as gear goes, on the digital cleaning side I have Steinberg Clean, the Waves Restoration Pack and the Sonic Foundry Niose Reduction bundle. Clean is a stand-alone application. Waves and SFNR are plugs that I usually run through Sound Forge. Sound Forge is my personal editor of choice for mono and stereo wanveform editing and mixdown pre-mastering, but you can use whichever editor you're most comfortable with. I also have more processing plugins in the form of EQs, analyzers, companders, verbs, delays and kitchen sinks that I can count. Again, use the tools that fit your hands the best and learn how to properly use them as part of the restroation and enhancement processes.
On the analog side, you'll want good PLL direct drive turntable with a quality cartrige and stylus, and with manul speed override available and a quality tonearm balancing mechanism. A high-mass tonearm, while pretty much out-of-favor with audiophines, is not a bad idea because it can often track the stratches and warps a bit better. Though that is a more minor detail that you probably don't need to lose any sleep over.
You'll also sooner or later want a more average (most likely belt-drive) one that can playback 78RPM sides. You can start with the good one and get the other one when you're client needs demand it, but when you can det a servicable belt-drive turntable with a reversable 33/78 stylus for under a hundred bucks, it's not hard to add to the inventory list

.
As far as a preamp for the turntable goes, any real good consumer preamp or integrated preamp will do a good enough job. It will be far from being the weak link in your signal chain for this kind of work as long as you don't skimp. It'd be nice to find an integrated preamp with dual phono inputs so you don't have to switch your turntables around, but that's a luxury that hard to find.
Oh, I almost forgot. Some nice quality pro analog gear in the form of tube compression, EQ, etc can put some nice final touches on your work, and for processing are often superior to all but the best digital plugs. I have not gone real expensive here (only because I can't afford to

), but a couple of real workhorse usints for me in this area are the ART PRO VLA tube compressor and the dbx2215 1/3rd octave graphic EQ with limiters. Not the greatest in studio gear, I'll be the first to admit, but I often use them to great effect in this area of engineering.
HTH,
G.