I'm very curious about 1l- removing cantrip damage scaling. I think the "light" version of it would be to make it class-level dependent, not character-level. Incentivize single-classing (although as per 1n you removed MCing).
How do your players feel about these house rules? How often do you run sessions? Capping scores at 18 instead of 20 is pretty interesting as well.
For 1l, no issues at all. The cantrips have riders which can be very useful. If you don't allow multiclassing, they would scale by class level automatically, as you noted. IMO, multiclassing and feats are the two greatest offenders when it comes to creating unbalance. Many of the feats are fine, or only require minor tweaking, and so we've used them still from time to time.
Frankly, they keep a lid on the game more. Take expertise, for instance. RAW, you can have a PC at first level with a +9 modifier to an ability (skill). The game is supposed to "run fine" just using DCs from 10-20, but at +9, especially if you have another PC who can grant advantage (via
guidance or the help action, etc.), the PC has a 75% chance against a DC 20, at 1st level? No, that is too much IMO.
So, make expertise advantage. Now you can still have a +7, which is awesome, but it brings it down to 64%, which is sort of the "established" success goal of 65% in many cases. Still high, but better IMO.
One of my favorite houserules is that healing magics, etc. only provide temporary hit points. Since you can't have more than a single source of temp hit points at a time, you can "improve" your condition if you gain higher temporary hit points, but you quickly realize you can never fully recover! Frankly, this alone makes things MUCH harder for the PCs in many ways!
Capping scores at 18 also helps with the bonuses climbing a bit too high. I know it is only a +1 difference to bonuses, but it also feels better when proficiency caps at +6 that abilities are +4 instead of +5.
If you keep feats out, it also forces players to place ASI's elsewhere as the cap 18 is reached more quickly than cap 20.
I'll update the post a bit later, as we also have a number of house-rules and systems in place to
aid players and their characters. One instance is upcasting spells. If you upcast a spell, you gain the maximum benefit from the additional spell levels, no rolling involved. For example, casting a
cure wounds at 2nd level isn't 2d8+ability modifier, but d8+8+ability modifier. It makes upcasting an attractive option IME.