If Hit Points are a measure of skill level, luck and other factors, in addition to raw ability to withstand injury, it makes little sense for healing spells and the like to repair proportionately less damage to a character with lots of HP. The proposed system below also negates the increasing need for parties to be loaded down with potions and healing spells as they gain in levels and HP.
Spells and their equivalent potions will always restore at least a minimum number of HP; see the table below. Alternatively, any Curing magic can be used to restore lost Fatigue, but the spell does not then also heal wounds.
As the amount healed by Lay On Hands already increases when the caster improves in level, it's not changed by this system.
Round to the nearest HP when calculating healing. Note that Subdual Damage heals completely in 30 mins; any magical healing also restores all lost Subdual Damage.
Again, it seems illogical that a character is able to use a club but not a mace; the two weapons are very similar. Here's an answer.
A Weapon Group is a set of weapons wielded in a similar way; it costs two Weapon Proficiency Slots to become proficient in an entire group, so that all weapons in the group are used at no penalty. Note that there is an overlap between some groups, and that some weapons are not related to any other, and so are not in a group. Warriors may only take Specialisation in one weapon (costing an extra slot as usual), and gains no advantage when using other weapons in the group.
If the DM wants to allow it, characters who have a Weapon Group Proficiency which includes weapons their class is usually unable to wield can use those weapons, but at the standard non-proficient penalty.