I am now further into the game (lv 25). Let me attempt to answer my own questions in case it is helps other new players:
(1) The items and spells offered to you determines your strategy and preferred army. Keep options open.
(2) Some really long-lasting useful units (available since early game) are:
Royal snakes: no retaliation, hit hard & reasonably fast. Must combine with the frog wife (ignore her for a while and she will turn into a frog). Even better with Grand Druid's Staff and the Ring of Snake King. Swap out the staff with better weapon artifact later, though. Always sold in the Alanria cave.
Inquisitor: powerful undead killer. Resurrection special ability keeps the army healthy. There is no guarantee of supply, though.
Evil beholders: mind control is awesome when followed with the Hypnotize spell (the effect will last to round 3) as a battle opener. Available in Freedom island or the latest dwarf underground.
(3) Some long-lasting useful spells are:
Distortion magics - most of the best spells are in this category. Max (lv 3) ASAP.
Hypnotize: great battle opener, especially useful if followed by sacrifice to replenish troops.
Sacrifice: (chaos magic) convert army A into B. Great when followed with Hypnotize as that army A comes from the enemy. You can always buy hordes of peasants and kill them while battling some weak enemies. Get Chaos lv 2 later so you can gain dragons this way, too. Sacrifice is the only way to keep a healthy stack when it is not available for sale (or sold out).
Phantom: clone your best/fastest stack and rush them into the enemy. Note that skeleton archers can dispel them with their normal attack.
(4) Some useful rage spirit skills:
Rock spirit - develop ground spike as much as possible (available at lv
. At the end it deals 1000 damages to all targets (double for mages). The wall is nice for delaying an advancing monster stack - don't bother upgrading the wall as it will be demolished easily anyway.
Poison spirit - evil shoal is great for early-mid game. Glot's armor is nice when you want to save some troops. Again don't bother upgrading it.
Ice spirit - develop Ice orb into the HP1700 version. It is a great battle opener as a great distraction and shooter blocker. Just drop it in the middle of shooters. The ice walls are great for blocking the AI.
Death spirit - develop Black Hole to the fullest. I am not very familiar with Time Back yet - dunno whether it is useful.
(5) Level up priority
Level 1-5
Attack > Rage > Mana > Leadership > Defense = Intelligence
Level 6-30
Leadership > Attack > Rage > Mana > Defense = Intelligence
(6) Skill priority
Might line:
Good skills: Anger, Tactics, Onslaught, Night operation
Mind line:
Good skills: Reserve
Try to max Learning and later on the Glory line. Get Diplomacy lv 1 (or even 2) to save you trouble from restocking.
Magic line:
Magic makes huge differences in battle even for a warrior. There are many good skills:
Distortion (lv 3 ASAP), chaos (lv 1 is enough. Get lv 2 when you have dragons), mana regeneration on the map, mana regeneration during battle, knowledge (+mana).
(7) General tips
- Troop conservation is the key. Use your wits to always cut down the loss to minimum, while still having a decent amount of rage and mana for the next battle.
- Fight the weaker enemies and avoid the stronger ones if you can. A very powerful foe can wipe out half of your stack - some precious units are hard to come by.
- Carry a large reserve of die-easy units in your starting roster (royal snakes, for example). So their number is always maxed.
- There are very few rage potions/recharge point compared to mana potions/springs. Therefore, keep all the un-upgraded items and the Goblin castle and use them ONLY to recharge your rage when needed.
- You can find better items than your own children starting from mid-game. There is no way to discard children unless you divorce your wife. Remove all items on her first.
- The AIs have a taste for the decoy units (hypnotized, ice orb, phantom, totem, etc.). Use them to absorb the damage.
- Melee attack accumulates rage points faster than ranged attack.
- Hire some high-initiative, high-speed units. They allow you to cast spells first, and while waiting they can act twice in a row.
- Do as many quests as possibles. There are great rewards (items, runes, new creature for sale) in many quests.