I haven't found longbows to be more expensive than recurves. There may be more entry level recurves available (around $100 - $150) just because there is more demand for them at that level, but at the high end (say $500 and up), I think recurves and longbows cost about the same for a given level of quality or reputation of the bowyer.
Longbows and recurves are very personal choices. You could start with one or the other and shoot it all your life, or you could end up with a wall full of both longbows and recurves, some of which you still actually shoot (but the rest hold some fond memories). Generally speaking, a longbow is considered harder to master and shoot accurately than a recurve, which is why they have their own division in most archery tournaments. But you're judging yourself against other people shooting the same type of bow, just like you wouldn't compare either bow to the accuracy you would get shooting a compound with sights. Don't get me wrong; unless you turn out to be a very good shot indeed, there will be longbow shooters who will whip your tail no matter what kind of recurve you're shooting.
Bowyers will publish the recommended draw lengths for their bows. For example, a particular 60" bow might be specified as working best for draw lengths of between 27" - 31". People might want a shorter bow if they intend to hunt from ground blinds or in brush, or they might want a longer bow for increased accuracy in target or 3D shooting. You should probably never buy a bow where your draw length is longer than the recommended range, but it is okay to buy a bow where your draw length is less than the recommended range if you like shooting a longer bow.
Most modern bows have an arrow shelf which is cut in so the arrow rests close to the midpoint of the bow limb (centershot). The bow will accept a wider range of arrows without getting bad arrow flight, and the shelf helps with accuracy. Primitive bows, commonly made from one piece of wood (self bows) may have some kind of minimal shelf stuck on the side of the bow, or no shelf at all. You're not going to be able to shoot these bows as accurately as modern bows, but that really doesn't matter if what you are interested in is shooting primitive bows.
I think Bear's rule is fine, but I would expand it to say hold at full draw for 10 seconds without straining or shaking, and be able to repeat that maybe 5 times with a 1 minute rest in between pulls. I think the 5# heavier is because you will gain some strength as soon as you start shooting. Don't kid yourself though, you will learn much faster and shoot much more accurately if you start with a bow lighter than you need rather than one heavier than you need.
Usually there are bows available to shoot at trad expos; however, I don't know how much good that is going to do you if you don't know how to shoot yet. I bought a bow at a trad expo I went to recently because I thought it shot great, and now I wonder why I did it, and I have been shooting for many years.