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.
For proportional Healing, round to the nearest HP. Spells and their equivalent potions have a minimum HP value they will restore; see below. Fatigue expended can also be cured with a Cure Light Wounds, but the spell does not then restore lost HP from wounds.
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 sabre but not a scimitar; 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.