Hey, thanks for playing LoTRO and congrats on rolling an LM. Al of your questions are covered in detail in previous threads, so I'm not going to go into deep detail here. My suggestion is to read the "stickied" posts on the Lore-Master forum page, and find other "New LM looking for help" posts.
Virtues: Pick whatever makes sense, like you've been doing. There is no real right or wrong here.
Interruptions: General rule - If a skill has an induction time, it can be interrupted. You can check the induction time of a skill by hovering your mouse over the skill and reading the tooltip. Melee skills like Staff Strike and Staff Sweep are immediate, and cannot be interrupted.
Pulling: LM's usually rely on "root pulls." Cracked Earth is a popular skill for pulling groups. You have to kite for a bit before the root takes effect, though. Herb-lore is another way to root your enemies. Then you can attack a single target, and the rest will remain rooted and won't be able to attack you.
Skills I use the most: Blinding Flash, Light of the Rising Dawn. All LM's are different. My personal playstyle involves a LOT of stuns and dazes. Trick is to make sure your DoT (damage over time) skills don't break the daze.
Flanking: flanking is like a critical hit from your pet. When the enemy is flanked, certain skills get extra bonuses. Wizard's Fire will heal you, Staff Strike deals double damage, and Staff Sweep will grant power over time. So yes, flanks are incredibly useful.
Pets: Lynx is great for mowing down solo landscape mobs, yes, but not much else. Raven is big - especially at endgame. Most of your decent damage skills are fire damage, so Benediction of the Raven comes in handy by making your enemies vulnerable to fire damage. The Raven can also reduce ranged damage by 50%. Combining this with wind-lore means that ranged mobs do 0% ranged damage.
Yellow/Red/Blue: These refer to Class Traits. Red increases your damage output, specifically Fire-based skills. Yellow is CC (Crowd Control) focused, and Blue is a hybrid Healing/Pet focused line. Most LM's go with Red and Yellow. Depends on your playstyle.
LM Trainers: They will give you class-specific quests at 15, 40, and 50 iirc. That's why they have the greyed-out ring.