Question 1:There are a number of things that can trigger due to the death of a creature. If we are attacking a minion, we know that our attack would deal enough damage to kill a creature, or if we simply suspect that our attack might kill a creature, we might want to make sure that we don't kill it in a square wherein it's death can serve as a trigger for one of those things. As such, we would like to slide our opponent before dealing damage, so that it is not in range when it dies. Is it possible for us to resolve the slide before resolving the damage?

Eldritch Strike Warlock Attack 1
The dire power of your attack drives your enemy before
you.
At-Will ✦ Arcane, Weapon
Standard Action (special) Melee weapon
Target: One creature
Attack: Charisma or Constitution vs. AC
Hit: 1[W] + Charisma or Constitution modifier damage, and you slide the target 1 square.
Increase damage to 2[W] + Charisma or Constitution
modifier at 21st level.
Special: When you take this power, you determine whether you use Charisma or Constituion for the power's attack roll and damage roll. This choice remains throughout the character's life.
This power counts as a melee basic attack. You can choose this power instead of eldritch blast as the power associated with your Eldritch Blast class feature.

Eldritch Strike is simply used as an example power, because it is an at-will that does things that we might want to apply in a different order.

Relevant section of the PHB:
ATTACK RESULTS
When you make an attack, compare your attack roll
to the appropriate defense score of the target.
✦ Hit: If the attack roll is higher than or equal to the
defense score, the attack hits and deals damage, has
a special effect, or both.

Question 2: Eldritch Strike specifies that it "counts as a melee basic attack." This then allows eldritch strike (since it counts as an MBA) to be modified or affected by anything that would then modify a melee basic attack, I presume?

Question 3: If a Feat, Class Feature, or another power adds something to an attack that happens on a "hit" can we then treat the power as though it is producing that effect as part of it's Hit line (or Effect line, etc. depending on the wording of the element in question)? To further the question, Impaling Spear (Martial Power 2) allows a melee basic attack to target Reflex or AC. Would it modify our Melee Basic Attack to read: (or Reflex, being the addition to the power text) and if, when using the power, we chose to target reflex, it would then count as an attack targeting reflex, for the purpose of producing any effect that requires an attack that target's reflex. Is that correct?

Melee Basic Attack Basic Attack
You resort to the simple attack you learned when you first picked
up a melee weapon.
At-Will ✦ Weapon
Standard Action Melee weapon
Target: One creature
Attack: Strength vs. AC or Reflex
Hit: 1[W] + Strength modifier damage.
Increase damage to 2[W] + Strength modifier at 21st level.
Special: You can use an unarmed attack as a weapon to
make a melee basic attack.