There is no "rulebook" on what wattage you should vape at on any given build , it's ALL personal preference .
Rule of thumb is start low and work your way up until you hit the sweet spot where you like it best . Others peoples preferred power levels are just that , other peoples preferences , find what you like .
For the OP: To illustrate herb's point a bit here I'll convey my current set up.
I am using a stock 1.5 ohm dual coil in a Smok T-Dux 3 tank. Presently, I am running at 8.5 to 9.5 Watts.
Of a morning, not quite up to a full 9.5 Watts dumping vapor into me. Usually by mid afternoon I can
do that.
If I use an RSST, a genesis style tank, I may use a 0.9 ohm coil and use around 15 - 20 Watts. I can do that because
of how that tank is designed. Also the air flow hole on that tank's cap is drilled out to about 1/16th of an inch. It
brings in plenty of air. The RSST also hammers me with vapor production.
I get fair vapor from T-Dux, ARO tanks. I never get OMFG Cloudz Bra type of vapor from the evod style tanks.
They do provide enough that I feel satisfied in using them. The RSST is more of a special treat use tank. I am awaiting
a tank which will fit in the middle, daily use and special use. It will be on a squonk set up and mechanical.
Using a mech, not going to be sure of wattage. Believe we can get something called 'kicks' that protect against shorts
to a point. Not sure if I'll do that or not. It seems appropriate battery and mod usage also reduce short risks as well.
Point being, it's personal preference.