You can certainly cbet too often, but I think most live and recreational players, being too passive, cbet way too little. Like a lot of other poker decisions, it's situational and villain dependent. But as a general rule you want to cbet any ace flop, and dry boards that likely missed villain's range. And of course always cbet for value when you have it, the exception perhaps being against a LAGtard who you know will bet into you and hang himself.
Generally speaking, I agree that a 70-80% cbet range is probably where you should be. If you cbet too little you are going to get exploited by good players stealing you blind. You'll be the one playing your hand face up, i.e cbetting only when you hit. You have to remember that most of the time, villain didn't hit either. Presumably your preflop initiative was due to a strong hand (at least that's what you hope to convey), but if you don't feel good enough to cbet most of the time, people start categorizing you as a loose-passive type that can easily be run over.
Likewise cbetting 100% is going to result in playing back at you and putting you to tough decisions after you've spewed into a bloated pot without improving. But if you're not playing too loose in the first place, cbetting is seldom a bad idea outside of specific flop textures. And of course, you adjust to the game at hand -- if you're at a table that always folds to your cbets, then widen your range and cbet 100%. If people constantly call and raise your cbets, then be slow down. Remember that an important key in poker is to assess how everyone else is playing, and try to do the opposite.
I'd say AK is almost always good for a cbet, especially against a flop like that. You have overcards and blockers to the broadway straight if villain has AQ/KQ/QT type hands. Again, villain dependent, but if you get called and don't improve on turn then you can slow/shut down.
Also a couple other observations. I assume you're talking live, because yours sounds very much like a live player mentality, which is quite different from online. Online games are tougher than live games at similar stakes, and tend to play much more aggressively. Live games have lots more limping and passive play than online, so it tends to be a lot more obvious when they have a hand. Take your example of opening for 5x. Why? Outside of specific situations that's way too much for an online game. Do you open your connectors and small-pp PP's for that much as well? How about QQ+? If your bet sizing is based on hand strength, that's a huge tell.