To add to the discussion and provide a bit more information as per the original question:
The numbers on planes refer to the size - the higher the number the bigger the plane. There are then an additional series of planes for a variety of specific tasks, or difficult timbers. Further, some planes are referred to by the orientation of the blade as well - bevel up or bevel down for example. The numbering system typically goes from 1 (small) to 7 (big - for flattening boards) and just to be confusing each of the numbers also has a name traditionally associated with it. Rather than list them all here, this is a pretty good link explaining things:
http://www.popularwoodworking.com/tools ... nch_planesWhisper it quietly, but some people have been known to collect planes as well as use them. As you correctly surmise, it is not necessary to have one of each. Some will be better suited to particular tasks than others and some of the functions of the specialist planes might actually be impossible with a standard bench plane.
To get started however, as stated above, a block plane for small work and finishing work will be helpful. A more general purpose plane for larger timbers would typically be a number 4 or 5. Some people recommend a bevel up plane as a general purpose plane - it really depends on what you want to do in terms of work. If you want to use highly figured exotic timbers with gnarly grain then this would suggest a different plane to working in pine, or a plane suitable for shooting. If you can provide more detail on the type of work you propose doing then you you might get some more specific advice.
Also as mentioned above - a plane is only as good as the edge you can put on the blade - the sharper the better. There are a myriad ways to put an edge on a plane blade, some cheap some expensive. Each has their advocates and detractors and the arguments can be fierce! It is really a case of trying a method and seeing if it works for you - none are a magic bullet solution for everyone. Given this, it pays to start with a cheap method (eg scary sharp on wet and dry paper, or the system from Workshop Heaven) and work upwards.
A final word on 'old' versus 'new' planes. There is a belief that 'old' is better. There is also a belief that 'cheap' is a false economy. Cost is always relative. You can get old planes that have non-flat soles and they will work poorly. You can get new planes that are relatively cheap that work well. I do not have much experience of 'old' planes, but buying on e-bay or boot fairs can lead to bargains or can be a pain to fettle. Buying new, most planes will require some fettling. Good (but expensive) makes include Veritas, Lie Nielsen, and if you can still get them, Clifton. The QS range from Workshop Heaven and the Wood River makes are cheaper and almost as good quality and are now pretty much standard for new woodworkers who want a compromise between quality and cost. I cannot comment on the new Axminster planes as I have not tried them. I would not recommend just nipping into B&Q and picking up a Stanley no4 however.
You can put new blades in old planes, and different steels for plane blades also have their supporters and detractors. This is pretty much a 'suck it and see' preference for the individual depending on how long you feel an edge lasts on a specific tool and whether the quality of finish is acceptable.
A well tuned and set-up plane is a joy to use. A poorly sharpened or fettled plane is a pain in the backside and can cause you to give up woodworking altogether!
Steve