Bloody Aegis, honestly isn't to powerful if you deliver debilities at least irregularly with normal hits~ (and certainly, don't let them block a debility by using Bloody Aegis. If you're delivering one, and they choose to use Bloody Aegis to avoid damage; they get two.)

I do it just about any time they are against something messy, massive, or they take a particularly brutal hit. I've also provided 'scarred' to someone who wasn't wearing a helmet when their armor took all the damage from a hoard of monsters trying to claw them around a shield in a narrow tunnel~

If Debilities ONLY exist because Bloody Aegis is used; then yeah.. it could be pretty strong. If people get Debilities naturally from hard moves by the DM? Then it's pretty balanced in my opinion.

I use a hex-map for travel; and I roll a 1d20 to determine how many 50 mile hexes (1 day of travel by foot) PC's cross before bumping into a random encounter:

Town, point of interest, monsters, wild animals (worth noting that they can create great encounters on their own), a corpse left in the wild, a ruin, NPC's-- whatever.

If the players roll well on their 'scout' check, then they have the drop-- if they don't? The encounter has the drop on them, or they discover eachother at the same time (surprising the fuck out of eachother -- or neither being surprised.)

It's also a way I've found to get the 1d20 used in Dungeon World.

If players are using the road; I may give them an encounter anyways~ just because they're going the most traveled way.

1) It's best if you take it first -- but if you want to be Half-Elven, you'd do it ASAP; however the ability to cast spells is not always an important thing to have. Magic Missile for instance (from wizards) doesn't get stronger the higher level you get.

2) Clerics have several useful abilities, such as Turn Undead that are pretty useful. Spellcasting is not the only thing that makes Cleric's useful. While elves cannot be clerics (but CAN be "ranger/clerics" as you put it) -- I use this as more of a cultural difference between the races.

3) No, they can take it. There is no such limitation. You can get whatever you want unless the limitations are expressly stated. One thing I like doing with my fighters though.. is going:

Scent/Taste of Blood
Merciless/Bloodthirsty
Multi-class: Viper Strike/Viper Fangs

Dual wielding champion of ass-kicking prowess = 1d10+3d8 damage. The greatest weapons master that ever lived.

*Nobody* wants to tangle in hack and slash range with a fighter that does 19 damage average with hack and slash.

You can't do that if you go with Cleric Spell-casting as a fighter. A combination of fighter penetration and a few other abilities.. and a blacksmith upgraded signature weapon, and if you can touch it (a big if, given the size of some enemies) -- you can kill it.

The fighter can be a true wrecking ball without spell-casting; most of the classes are at their most amazing if you capitalize on their strengths, rather then trying to get exotic-- although given the narrative nature of dungeon world? Ultimately, it's about the kind of character YOU want to make.

There is very little min-maxing in Dungeon World, because it's all relative to how a situation plays out. 1d10+3d8 with 4 piercing is not very useful against a flying, fire-breathing dragon running you down while you're horse-back riding on the road~