If the creature becomes a 4/4 Shark and then the cracks become completely covered later in the turn, the creature won't spontaneously become an 8/8 Octopus
Whats your experience with lesson and learn cards
Which of these approaches is better is a very contextual question, and not really one that Im looking to answer right now
However, thats contingent on your ability to turn on freerunning, which requires you to play assassins or a commander that can consistently deal combat damage
While most likely to see play in cEDH, Ive seen enough shenanigans with cards like Enduring Renewal to respect the combo potential Wild Cantor brings to the table too
It gives the enchanted creature +2/+2 and haste, and when it enters the battlefield, it activates another combat phase