I just squirt it in until its just below the air holes. Normally the cotton soaks it up a few times until its saturated enough to hold some juice in the well.
theres no set wattage. it will vary due to many factors:
how well its wicked, type of cotton, style of coils (claptons, aliens, twisted, kanthal, nichrome etc, etc), whether you like a warm or cool vape, liquid you are using, how much airflow there is and so many other variables.
start low and work your way up. try 35-40w as a start maybe...
the amount will vary with the size of the juice well which differs from dripper to dripper. its a case of experience will tell you how much you can put in at a time....
one thing to be more wary of with the tsunami, is that it is bottom airflow, so if you over drip it will leak out the airflow slots on the base.
top airflow drippers tend to be a bit more more forgiving with regards to over dripping..