You can find a lot of information about possible values in the ValuesList.txt in the stats folder (if you extracted that.) Otherwise, I and others will be posting more about doing stat stuff soon. Min and MaxAmount are how much the item stack to (weapons never stack I think). Priority is drop chance I think? Just keep it to 1 I think. Flags include things like ChillContact, BurningContact, Unbreakable, BurningImmunity, etc. Here's a list for those:
If you put an existing template into "Using," then basic stuff (like weight, min/maxamount, priority, etc.) will be filled out. So if you were making a new 1 handed axe, you'd probably inherit from _Axes (or whatever the base stat entry is).
This is for skills, but a lot of the stuff in SkillProperties applies to ExtraProperties for weapons.
value "FreezeImmunity"
value "BurnImmunity"
value "StunImmunity"
value "PoisonImmunity"
value "CharmImmunity"
value "FearImmunity"
value "KnockdownImmunity"
value "MuteImmunity"
value "ChilledImmunity"
value "WarmImmunity"
value "WetImmunity"
value "BleedingImmunity"
value "CrippledImmunity"
value "BlindImmunity"
value "CursedImmunity"
value "WeakImmunity"
value "SlowedImmunity"
value "DiseasedImmunity"
value "InfectiousDiseasedImmunity"
value "PetrifiedImmunity"
value "DrunkImmunity"
value "SlippingImmunity"
value "FreezeContact"
value "BurnContact"
value "StunContact"
value "PoisonContact"
value "ChillContact"
value "Torch"
value "Arrow"
value "Unbreakable"
value "Unrepairable"
value "Unstorable"
value "Grounded"
value "HastedImmunity"
value "TauntedImmunity"
value "SleepingImmunity"
value "AcidImmunity"
value "SuffocatingImmunity"
value "RegeneratingImmunity"
value "DisarmedImmunity"
value "DecayingImmunity"
value "ClairvoyantImmunity"
value "EnragedImmunity"
value "BlessedImmunity"
value "ProtectFromSummon"
value "Floating"
value "DeflectProjectiles"
value "IgnoreClouds"
value "MadnessImmunity"
https://docs.larian.game/Skill_creation