I use 26 gauge titanium because it's a bit more robust and easier to work with than the thinner gauges for me. I also shoot for around 0.25Ω, but I also normally run dual coils which means each coil needs twice as many wraps. For my Silver Play that means two coils, 2.5mm ID, and 10-12 wraps would put me at a total resistance around .2-.25Ω... for a single coil that would mean 5-6 wraps. Then start the temp at 350°F and bump it from there until you're happy with it.