1. Card states that for the combat check you roll strength melee (which is d10 +3) + 1d8, since the rules state you can only play 1 card type per check, you just get the 1d10+1d8+3 (if you don't discard it)
2. You can only use the longsword for your combat check. So any time you roll for a combat check you can use the longsword. You can't roll for other people's combat checks. But you have your power that gives them 1d4 for their combat chec,k.If you encounter a monster on another player's turn (i.e. goblin raiders barrier) then you can use the longsword for your combat check when you are forced to encounter a goblin (in this case).
Evolusi is correct here. With a good amount of "melee" weapons, you can have the option to discard them for an additional die. So it may look something like this:
(1d10 +3 base) + (1d8 weapon reveal) + (1d8 weapon discard)
However, it's really important to note that as Valeros, he can RECHARGE his weapons instead of discarding when they are played, as stated by his power.
Valeros has a good amount of weapons in his deck, so it wouldn't hurt too much to make sure a baddie is down for the count and recharge a card (this is all depending on the situation of course) since you don't have to discard. Valeros is stronk! (in combat)
Thanks for your help! :)