With airbrushing there really is only one direction you can go in and that would be with a graphics tablet. The sweeping smooth lines and gradual range of tones when airbrushing lends itself to the use of a tablet. The arm and wrist motion of true artist who work with a pencil would need such a device to recreate the strokes onto the digital canvas. Tablets can replicate the stroke, pressure and angle of brush or pen. They can even give you the freedom of different brush heads such as a splayed brush, line brush or even wet brushes for mixing paints and colours on the the page. With such sensitivity it is easy to forget its not a real pen.
Not so much though when it comes to the restorer who pieces back together their images from existing element within the scene. This technique could easily be done with a pen and tablet but so often is performed with a mouse. Perhaps with aim of precision mouse mat and a laser mouse to get a much control as possible.
Should you wish to take the plunge and get a graphics tablet for your work there are many manufacturers on the market providing cheap models to those which cost a small fortune. Even touch screen your draw directly onto as it were real paper and pens!
To make up your own mind which manufacturers to go for here is a short list, Wacom, Hanovan, and Trust. Wacom hold the place in many designers hearts as they have without doubt been around the longest, but newcomers Hanovan with their ArtMaster III series have a strong contender. Trust sit at the lower end of the range but still with great equipment with the Trust Canvas Widescreen. Whichever of these you choose be sure to check the manufacturers websites for compatibility with your system and read reviews to help make up your mind which one is the best for you. Its been said if money is no object then go for Wacom.
Photo restoration is without doubt a service that will require specialist hardware particularly where emulating the pen stroke is concerned. If you decide to break out into the market, prepare yourself first with the adequate skills and then obtain the hardware, for if you skills do not match up to the other better photo restoration companies out there then your specialist equipment may be a waste of funds.