With two identical coils at 0.36-ohms each, you should get a total resistance of 0.18-ohms or half of the resistance of one of the coils when they are installed in parallel. Not sure why you are getting 0.29-ohms, but it may be that the coils are not the same resistance, or you have a loose connection on one of the coils. Check to make sure all of your leads are tight. Sometimes the screws loosen after a few heat-cool cycles.
Wattage is very personal and subjective. I would start low (20-30W) and increase slowly (5-watt increments) until you get the vape you are looking for. Don't rush, just slowly increase and test at each increment to avoid a dry hit or burnt cotton.