I use the term mystic archer to refer to a no-melee archer who uses supportive magic as back up. This is not a ranger who backs themselves up with a blade. It is not a 'mage with a bow' who relies on elemental destruction magic and uses a bow simply to start long range fights or as a poison delivery device. That is not to say that either of those other two types of characters are not viable.
To illustrate the difference though, my mystic archer's 'kill break down' probably looks like this:
90% bow, 6% illusion spells (enemies killing their friends), 2% summons (mostly distractions), 2% touch damage spells
As you can see, the emphasis is on archer, not mage; yet with no melee.
Basic tactics for differing situations look like this:
-Normal: Long range poisoned sneak shot.
-Dispersed crowds: Snipe the farthest first and stay in the shadows. Repeat.
-Tight crowds: Mind control spells to get the crowd to thin itself to one. Snipe the survivor.
-Underwater: Block with your bow and cast touch damage spells (normally absorb health).
-If cornered: Block with your bow as you immobilize your foe with a spell (command, calm, paralyze…), then open fire with your bow.
-If charged: Stop the charge with an illusion spell, then open fire with your bow.
-Panic button: Invisibility, slip away and reapproach for the snipe (combining a cheap summon with your invisibility spell makes this both easier and more fun).
Important capabilities (Nothing to do with major skills): Bow, poisons, weakness to poison, drain speed, detect life, a slow and methodical patient playstyle, mind control spells, invisibility, Cobra's Dance (from the Serpent Birthsign Stone), blocking with a bow, touch damage spells.
This is definitely a 'glass cannon' character.
I try to avoid specific build recommendations regarding mundane things such as major skill selections and such, because it just depends so much on how you want to play and level.
Sounds excellent, I'm going to make one now and see how it goes. I plan on going with these major skills taking your post in consideration : Sneak, Marksman, Illusion, Conjuration, Destruction, Alchemy and Light Armor
I'll level Alchemy, Sneak, Illusion, Light Armor and Conjuration to 100 before starting the main quest/shivering isles and I'll level up marksman to a high level on the Peyrites shrine followers