This one has always been a bit of a handwave because Linked powers need to have the same range. By the book, with just the main book, you'd have to set up either Healing with the Reaction extra triggered by damage (or Triggered as long as your concept supports preparing the healing ahead of time with actions, and having your prepared healing able to be "disarmed" with skill checks) or Regeneration with a Limited (Source) Flaw so that it only works if you've done damage recently.
Outside of the main books, one of the Power Profiles did introduce Psychic Vampirism, which is a handwaved Linked as follows:
You mentally drain the target's vitality to replenish your own. Some Psychic Vampirism is also Insidious; the target does not feel or notice its effects until incapacitated by it. If the series features lethal damage, then draining targets past incapacitated leaves them dying. Psychic Vampirism able to heal Damage conditions as well as fatigue has a +1 modifier (removing the Limit on Healing). Psychic Vampirism requiring you touch the target has a -2 modifier.
Psychic Vampirism: Perception Ranged Cumulative Affliction (Fatigued, Exhausted, Incapacitated), Resisted and Overcome by Will, Subtle, Linked to Healing, Subtle, Limited (Energizing Only), Limited (Self Only) • 2 points + 4 points per rank
Rule 0 being what it is, to do whatever is the most fun, discuss it with your GM and see if they'll go for how you propose the power would work. Or, if you're the GM, use it. Just remember that anything the player can do, the GM can do, and potentially vice versa. And if you're the GM, and you're putting this on an NPC, and you forbid PCs from taking it, possibly because you feel it would be too powerful, consider whether it's just a form of GM Fiat and therefore something to pull for a Hero Point rather than as a discrete power.
"As you go to strike the bruised and bloodied Madame Nefaria, she stabs a dagger glowing black into your side. She rolls a 17 and hits. Roll a Toughness save. Ooh... looks like she's Staggered you and inflicted a -1 penalty. Take a Hero point as she heals the same due to her vampiric nature. Madame Nefaria's bruises fade as she laughs evilly and yanks the blade out of your side, her movements no longer pained and jerky."
The second part of your question, about Slam damage, has a canonical answer.
The Gamemaster may limit your base slam attack damage (before applying circumstance modifiers) by the series power level.
Example: Your hero flies into a foe, moving at speed rank 10. His unarmed damage (Strength) rank is only 2, so he uses his speed rank of 10 for the damage. Since he also moved his full speed to build up momentum, he increases his damage by +1 for a total damage rank of 11. If a base damage rank of 10 is too high for the series, the GM may impose a lower limit on his slam attack damage, applying the +1 modifier for the full speed move to the lowered rank.
So, in short, there's nothing guaranteeing you a chance to break PL, especially if you have a character built to avoid any of the damage from doing the attack.
As regards reaction "attacks" by linking it to movement, the onus is on the GM to police abusive builds like that.
The GM is the final arbiter as to whether or not a triggering circumstance is suitable for a particular effect in the context of the series. Caution should be used to keep this option from being abused.
Best Answer
Multi attack isn't ranked. Rather, an attack gets the Multiattack property, which increases the attack's power point cost by +1 for each rank of the attack.
It has three options:
See the d20Hero SRD's 'Modifiers' page for more details.
Single Attack:
Multiple Attacks
Covering Fire