Question about elemental weapons such as electric axe, voltage bow, cinder pipe:

Will I encounter monsters that take reduced damage from them, or none at all, from these weapons?
Are their elemental properties only in their bonus to element resistance they give?

Do they give any bonus damage to monsters "weak" to their element? In MM6-7-8 , the fire/cold damage is a bonus magical damage in addiotion to the weapon's base physical damage

I'm debating using my long bow +4 or voltage bow +2,
and between my electric axe +2 and scimtar +2

Thanks in advance.

MM2 doesn't have any on-hit properties of weapons; there's no bonus damage at all. All you get is the base weapon damage plus the enchantment bonus.

Also, later on it becomes easy to get any item up to +5, and possible to later get any item up even higher.

Worth noting that some of these weapons do special things when used as items, so try using them with the item command during battle. You can check the number of charges by casting Detect Magic IIRC, and you might also be able to check the properties of an item in the shop. Recharge item can give the item more charges; I've never seen it fail on an item with at least 1 charge, but make sure you don't go over 255 (integer overflows are a thing in this game).

Edit: If you find that your weapon isn't working against an enemy, it's not the weapon's fault. It could, however, be due to the sex of the attacking character.

Ahh that explains it, thanks.