I've had a new comment posted for a January 2009 posting -- The 18th Century? What's the Fascination? -- from a relative newcomer to the hobby, who asks about getting started, figures, and so forth. So, I'll say a few random words about my personal preferences and then turn things over to anyone else who might care to chime in here with further advice.
Both titles are available in recent reprinted editions at reasonable prices and filled with all manner of historically-based explanation and explication. In addition, the two books present detailed rules for fighting 18th Century battles. They also contain a variety of inspiring photos, useful information on painting figures, building your armies, creating scenery, etc., etc. There are, naturally, lots of other useful, more recent history and uniform books out there, but these two provide a solid starting point for anyone interested in the 18th Century in particular, or, indeed, wargaming in general.
There are many other good 18th Century figure ranges on the market (even some in plastic), in a variety of sizes and scales, but those I mention above are especially good if you prefer realistic human proportions with understated detail. Sadly, there are many figures on the market with strange anatomy, in overly dramatic poses. . . A definite a no-no for the 18th century. A few brands come to mind, but I'll keep those thoughts to myself for now.
Suffice to say, take some time examining samples from several different manufacturers before you purchase any figures in bulk. It will save you money, disappointment, and frustration in the long run. In any case, I'd suggest that you start small, say 150 figures or so, divided into five or six units with some supporting artillery, maybe two or three guns and crew. This will give you enough for a small tabletop army without it taking you several years to finish painting them.
But what about painting those figures? Well, that's very much an individual thing that you will learn through trial and error. There is much information on how to do it on this blog and, indeed, across the Internet, so I won't go into a tutorial this morning. However, I will say that even if your early efforts with the brush leave something to be desired, practice and determination will have you producing units of nicely painted figures before too many months have gone by.
The main thing to remember about painting figures is that you need to give it a try, be consistent in your efforts, and don't become intimidated into inactivity by the ranks of shiny, unpainted figures lined up on your painting table. The figures won't paint themselves after all! Neither should you become discouraged if your first few units don't resemble the museum pieces produced by professional painters. . . Ah, alliteration this morning! Finally, don't be afraid to experiment a bit with your own painting, to find the method that works best for you.
What uniforms will you paint onto those figures? Well, there are many different, good historical uniform reference books available, which will help you paint your units. Those by Osprey are readily available and don't cost too much. I also like Uniforms of the Seven Years War by John Mollo and Malcom McGregor, which might be hard to find now, but it is worth tracking down. The old titles by Fred and Lillian Funken are also worth a look as are uniform books on the American War of Independence and the French and Indian War in Canada. Lots of titles too on the earlier War of Austrian Succession, the War of Spanish Succession, the Great Northern War, and so on, depending on your precise area of historical interest. One thing about the 18th Century is that the era provides a broad array of conflicts on which we can base our tabletop aspirations.
Multiple wargaming interests are fine, but if you ever want to get anything finished in one area, it's really worth some honest reflection and hard thinking about your most consuming interests BEFORE you purchase figures and related supplies in bulk. Otherwise, everything will simply end up gathering dust somewhere because your time, money, and creative efforts are pulled in too many directions at once.
So, finish preparing and painting your basic 18th Century force of 150 or so figures first. Try them on for size in a few games. Learn some more about the different ways the actual troops of the era maneuvered and were used on the battlefield by their commanders. And if you so choose, it's a fairly simple matter to add a few more specialty units to you basic force. Hussars, pontoon, or engineering troops anyone? Or, if you've still got the itch to try your hand at another wargaming era, now is the time for those ancient Greeks and Persians, Napoleonics, WWII, Warhammer, 1930s pulp gaming, and on. . . and on. . . and on. . . ad infinitum. But finish your 18th Century project first before you start something else, guys!