Heedless Resurrection

No, as the kill is an additional cost and countering a spell never refunds costs already paid.

Killing a friendly unit is an additional cost required to play Heedless Resurrection. A countered spell does nothing and is not considered to have been played.^{[425.1.a][425.1.b]} Countering does not refund any costs paid to play a card, including additional costs.^{[425.1.c][425.1.c.1]} That cost is paid before the spell resolves, so the killed unit is not returned.

No, as the resurrection target must already be in your trash when you choose it, before the kill cost is paid.

When playing Heedless Resurrection, you must choose the unit to resurrect during step 2 of finalization — the "Make relevant choices" step.^[355.5] At that point, the unit you intend to kill is still on the board, not yet in your trash. "A unit from your trash" must be in your trash to be a valid target,^[355.9.a] so a living unit on the board cannot be chosen. The additional cost — killing a friendly unit — is paid in step 4,^[357.2] after all choices are already locked in.^[355.15]

No. The additional cost to kill a friendly unit is paid once, as part of playing the spell.

Additional costs like this are paid during step 4 of playing the card,^[357.2] not during resolution. Repeat makes the spell's instructions execute an additional time upon resolution,^[820.1.d.1] but does not re-run costs that were already paid while playing — "as you play me" instructions execute once, before the Repeat execution ever occurs.^[135.2.b.3]

No matter how many times Repeat is paid, the spell is only played once,^[820.3.a] so you kill only one friendly unit.