1) Ability Score Increases
I agree with many others here...
If I wanted to reduce (1) I would just require that you can only take a feat but not an ASI at those levels.
And if I wanted to completely remove them, then I would also disallow feats that have a +1 ability bonus.
If you only allow PHB feats, here are the max ASI you can get from feats:
Str +8
Dex +5
Con +3
Int +4
Wis +2
Cha +2
But this is theoretical... for example to really get that +8 Strength from feats, you need to be a Human Fighter (the only character who can get 8 feats), you need to blow 3 of those feats in Lightly/Moderately/Heavily Armors solely to get the ASI (you already have all those proficiencies), and you need to start with Strength 12 in order to end at 20 after 8 feats.
In general we have the option of changing the required lengths of short and long rests. However this does not only affect healing, but
every ability that recharges by resting.
So you could instead leave the resting rules as-is, and either ask the players to purposefully avoid making characters with lots of healing abilities, ban certain options such as Life Clerics, or prohibit learning healing spells in other ways than through your class spells list (e.g. bonus Bard/Warlock spells, Magic Initiate, multiclassing etc). An extreme approach might be to completely remove
Cure Wounds and
Healing Word from the game, but I don't think anyone has the guts to try that
Then obviously the game becomes more deadly. You can dial back the difficulty by lowering the encounters per day (or their difficulty), but this once again will make other non-at-will resources become effectively more abundant.