Head Gasket Issues. Head Bolts?

I saw someone saying prius c is safe from head gasket issues. I also saw someone talking about head bolt failure.

I've been chasing engine rattle with coolant loss issues and I think it's head gasket.
Check engine light came on and it indicated No 4 cylinder misfire. (tried switching the coil)

Car works pretty nice during the day when it's pretty warm (Los Angeles)
It does rattles here and there when I move the car after seating at the traffic light for more than 20 seconds. (meaning engine got cold and water seeped into the cylinder)

So my question is, is replacing head bolts or tightening head bolts (Maybe tightening 5 pounds higher for bolts near Cylinder 4? or tight all bolts little higher?) might solve this issues since it's very small?

I was going to do the valve cover gasket anyways. (saw oil on spark plug Threads)
It looks like It sits underneath the camshaft.
How hard is it to put it back? I am talking about aligning it correctly. Do I need a special tool?

 

Actually it can happen in 20 seconds (depending on the weather) I've watched mechanic explaining and people also replied with the same experience on youtube.

When it was raining in LA, it was happening pretty much at every stop light.
Now since the weather is a lot warmer, it only happens after car is parked for few minutes at night.

Spark plugs are new from the dealer.

I am refilling the coolant every week. I wish it was just from the exhaust like other person's said