For your own stack, have a consistent way to order your chips, like piles of 10 or piles of 20, and just count them sporadically.
For the pot size, I recommend against trying to calculate it. It doesn't sound that hard but there's pressure during a hand it's famously hard to do seemingly straight-forward but somewhat annoying things like recall preflop action and do some basic arithmetic. So don't. Just estimate it based on looking at it; the chips are all there. You will get better at estimating the net value of a bunch of spread-out or stacked chips with experience. Minor mistakes in counting will not break your game. If the chips are oddly placed, ask the dealer to spread them out a little. Don't worry about how that makes you look.
For other people's stack, ask them. Say, "how much are you playing", or "could I see your stack, sir?".