Gelders are useful to keep the damnable cats under control (although drawbridges work as an alternative, and females can't be gelded), shearers provide you with wool (which you need for moods, even if you won't bother using it for clothing). I personally won't bother with milking because I'm too lazy to write a script that manages it (and buckets are in short supply for a very long time), but it is useful to provide favorite food ingredients, as well as cheese (although you probably don't need as many cheese makers as you get via migrant waves).
Mashing roles (or professions, if you like) into fewer ones takes away control from those who want it, while only saving (some) players a few role selections when organizing dorfs. If you go the main (Premium release) route and let the game try to organize labor it won't matter at all if roles are specific or mashed into a small number of combination roles since you won't touch it anyway.
Prices will probably remain essentially untouched until the economy arc, which lies beyond Myth&Magic, and probably also Starting Scenarios (and not ruling out other arcs beyond those, and definitely not ruling out tangent arcs). Whether economy, which relies on transport, or moving terrain (which provides boats) that has close ties to the economy comes first seems to be something Toady is deliberating over. Anyway, if no decision is made about the order, there's a fair while before a coin toss is necessary to finally settle on that order.