1) When instructed or given the option to cast an MDFC, you can choose either side (if that side is castable under the given conditions). Mila being the front side, though, and being a creature, Pako will not receive a +1/+1 counter for that card. Because there's no casting here, only the front side exists as far as the game is concerned.
2+3) Yes. When playing an MDFC, you get to choose which side to play. As long as that side meets the playing criteria when played.
1. If Mila, Crafty Companion is exiled by Narset, Enlightened Master or Pako, Arcane Retriever, despite the inability to cast Mila, could I cast Lukka, Wayward Bonder instead (if the conditions were correct)?
2. Could I cast Tergrid, God of Fright/Tergrid’s Lanturn from the graveyard via Muldrotha, the Gravetide if I haven’t played an artifact/creature for the turn?
3. With Crucible of Worlds, can I play Sea Gate, Reborn?
2+3) Yes. When playing an MDFC, you get to choose which side to play. As long as that side meets the playing criteria when played.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)