Those are interesting ideas. If I do play with ability increases I'll probably implement something on those lines.
Another thing to keep in mind is that the overwhelming majority of bonuses that players get come before level 10. You're expected to have a 16 at level 1, so +5 to hit with the +2 proficiency bonus. You get two ASIs before level 10, and your proficiency bonus increases twice. You should have a +9 by level 10. However, between level 11 and level 20, you only get two more increases. You cap out at +11. The game is built around leveling the PCs out like that, so they'll feel like they're gaining a lot of power in the early game, but it tapers off.
However, HP (and the associated amount of healing you generally had) in older editions was built more like a long-term resource, being chipped away with every encounter during the adventure, unless something bad and unpredictable happened, or too many unlucky rolls. But in 5e it seems like the overall (expected) damage players take in every fight appear to be much higher, probably to compensate for the increase overall healing in the system. And I fear that simply lowering healing to 2e - 3e standards might not work.
I was actually looking for some guidelines to rebalance monster DAMAGE to a lower healing standard, and not the healing itself which is easy to do.
I know that some monsters haven't changed much in terms of damage. For instance the Bulette has about the same damage per round in 3e and 5e.
But some, like the Bugbear, went from 1d8+2 per round in 3e to a whooping 2d8+2+2d6 in 5e.
It's not
just damage. If you look through the Monster Manual, you'll find very few creatures have more than AC 20, while the first creatures with AC 20 have a CR of around 3. Like I said, it's really quite easy to get +10 to hit by level 10, while it's
very rare for even a PC's AC to go much above 22 outside of limited effects like the
shield spell. You get to the mid point of the experience table, and every attack hits -- especially with advantage being fairly easy to access! You miss a
lot less in 5e in general and HP values are much higher to compensate; that's why Magic Missle is so bad. You don't get hit so much that armor feels worthless, but you get hit
a lot, and there just aren't the complex defenses that you could put up in earlier editions with spells. Concentration makes a lot of spells and effects a lot less appealing and really limits what you can do, and attunement assures that you've got to pick and choose what items you really want.
I strongly recommend playing the game for one campaign to level 10 or so without modificiations. Modifying or limiting ASIs isn't going to break anything, but changing damage, hp, and healing is poking at the game's foundation, IMO. What you're suggesting is a
huge undertaking.
The game is built around 6-8 relatively weak encounters per day (much weaker than you'd see in earlier editions) and those are intended to nickel and dime the PCs. That's how the short rest classes (Fighter, Warlock, Monk) are intended to keep up, and how the game helps ensure the PCs won't long rest all the time. The encounters are also usually very fast and very short. Unless you're a Life Cleric, you probably can't keep up. It's a bit different, and not always intuitive to new players coming from earlier editions.