Before learning about ev and icm I'm pretty sure I was applying the concepts on some raw level. It just seemed like common sense at the time. More recently I've been trying to take a more mathematical approach to calculating ev using the 2 and 4 rule vs pot odds. Is this what most regs do to make +ev decisions on the fly?

I struggle with how to make +ev decisions in many scenarios. For example,

1. Effective stacks 25bb. Hero has K7. Readless villain. We check to river. Villian checks. Board is A59210

2. Effective stacks 25bb. Hero has KQ Readless villian. Villian bets 3bb, Hero calls. Flop: Q1010 Villain bets 5bb.

My gut tells me to bet smalls in hand 1 but calling hand 2 may be dangerous. Can anyone share a more technical, ev-based decision?

Eat advice I can give at this stage in your journey is to understand how spr (stack to pot ratio) affects your post flop decisions. Hand 2 is a good example. It could be dangerous but there is now 13bb in the pot, you have about 20bb behind so an spr of almost 1:1. Happy to stack off here with TPGK. If you had 60bb behind I would not stack off

Reading Flynn/Mehta/Miller as we speak. Thanks for advice.

Yes, it's a very good shortcut to estimate equity. Practicing with programs like Flopzilla can make u better at this way faster than any book etc does.
After a while it's more like "I feel i have 33% equity on that flop vs his range", no one makes deep calcs when having 3 secs to make a decision.