I've done quite a bit of restorations in the past and do more these days, with my upholstery work. These days, I do more A)chair, sofa, ottoman, etc. type furniture, than B) dining tables, armoires, dish cabinets, cupboards etc.
For A) I rarely use a machine. Mostly hand sanding, detailed work, lots of curved pieces, etc.
For B) I have a variety of sanders and the task dicates which to use. I see several suggestions have been offered and all good. A warming: Before using a belt sander on a large flat piece, learn well how much a belt sander chews up wood. I would advise: Never use a belt sander on a large piece. You are asking for trouble, unless you really know what you are doing.
If I were to suggest a first sander, it would be an orbital sander.
In the mean time, as Bill suggested, do some reading. Before buying many books, check out this link: http://antiquerestorers.com/Articles/MOST_RECENT_ARTICLES.htm
Scan through the main titles of this "outline" (format) to zero in on wood (or metal) topics/titles, get an idea of what articles are here. Get some ideas of what you are in for, in a specific field (wood and furniture items, maybe some metal furniture items). There is a wide range of expertise within these articles. Let these articles guide you to furthering your knowledge base, then later you can buy specific books, as need be.
Another suggestion: No one person can learn all the different finishing/refinishing techniques (.... and maybe wood repair techniques, as well. I often have to improvise). In starting out, learn 1 or 2 good basic finishing/refinishing techniques, i.e., master them, then move on to others one at a time, to further your finishing/refinishing abilities. Select your beginning projects to coincide with your skills and advance your projects as your skills advance. *This pretty much goes for any craft, skill and/or expertise.
One never stops learning, especially with all the info and resources available.