1. Tyrant is good.. any class is fine. Archers are the best if you want DPS, either Silver Ranger (Elf), Phantom Ranger (Dark Elf) or Hawkeye (Human). Critical is strong in Lineage 2 and bows can get some high critical damage. Silver Ranger = more critical hits, Phantom Ranger = more critical damage, Hawkeye = balance of both, but more tanky/hp.
2. Just pick whichever area suits you best. I personally liked Abandoned Camp and Ant Nest early.
3. You should have enough SP to level all skills.
4. Keep all crafting materials.
5. Selling stuff in private store. Or make a dwarf. Dwarves are the money machine in Lineage 2.
6. I recommend Shillien Elder (Dark Elf), Prophet (Human), Warcryer/Overlord (Orc), or Elven Elder. Shillien Elder is more of mage support/heals. Prophet is more for buffs and physical damage. Elven Elder is more for defensive buffs and defense, along with heals. You pick what you want. That is not all of the buffers either, there are Swordsingers and Bladedancers which are critical to a complete party as well. However, for dual boxing, the first four I mentioned above are what you would want since they have heals to keep you going.
The difference between a warcryer and overlord is that a warcryer has party-level buffs, while Overlord has clan-level buffs. So, any buffs a warcryer casts only helps his/her party, whereas any buffs an overlord casts impacts every clan member within range. If you want your overlord to be useful he would have to be in a clan with your character.