does my merc have to hit or last kill a monstert for his gold find to take effect or does it automatically add to mine just by him being present with additional goldfind?

Works like magic find:
You kill the enemy: your gold find
Merc kills the enemy: your gold find + your mercs gold find

It works exactly like you: he kills, you get the goldfind bonus.

HOWEVER, and it's important to understand: if you're a Barb, a large chunk of your finds come from Find Item, and Merc Goldfind DOES NOTHING there.

So in reality, Merc Goldfind is roughly only 50% as effective as Goldfind on you (even more true now with Find Item being even better since 2.4).
It's generally better to build the Merc not for Goldfind but for pure clearspeed, and you focus on Goldfind yourself.

PATTERN
TYPE: Claw
RUNE ORDER: Tal + Ort + Thul
+30% Faster Block Rate
+40-80% Enhanced Damage (varies)
10% Bonus to Attack Rating
Adds 17-62 Fire Damage
Adds 1-50 Lightning Damage
Adds 3-14 Cold Damage
+75 Poison Damage Over 5 Seconds
+6 to Strength
+6 to Dexterity
All Resistances +15
Assassin exclusive Runeword that might be just a perfect weapon for leveling your character that primarily utilizes the Martial Arts Tree. It costs nearly nothing, as most of the Runes can be fairly easily acquired, and Pattern itself offers quite useful bonuses, both defensive and offense-wise. The added damage of four different types will surely come in handy when progressing through Acts, and as a weapon, it also offers quite a bit of defensive-oriented stats like Faster Block Rate, Attributes, and Resistances

there a lot of Fire Blast, need just Craft Helmet with two sockets, like Grim Casque (Sapphire) - and just pull Nef-Tir under.