I was hoping someone knowledgeable would answer - but I give up and will respond my self instead.
Converting arrows is more or less wasteful - you can find lots of arrows of all types. Putting a lot of points in the skill trees for specific types of arrows limits you - what if you run into mobs resistant to different types of damage? But it isn't THAT expensive to forget and relearn skills so putting points into an arrow you happen to have a lot of and find very useful is fine - you can switch later when you decide a different arrow works better.
A key decision is bow versus crossbow since those are different skills. I would skill-up for the best bow/xbow you have or can buy - and if you later get a uber bow of the other type switch around. Note that xbows tend to require higher strength to use and their damage may be governed partly by strength - regular bows may be governed by agility.
I don't play archers much - find them too wimpy - so hopefully others who know more will reply but something about a post with no replies geases me to answer (and Kiya and Raze and lately Arianna don't leave many).
