I used FLUX Studio. You have to go to the expert tab which is found in the advanced settings. There you will find a huge listing of settings that can be changed, and that is where I made my adjustments. Setting the width to 200% of the nozzle diameter (which is 0.4mm) gives you a bigger extrusion which increases the probability of it sticking to the build plate. And yes, you can set the initial layer height to twice the normal layer height in this tab as well. My normal layer height for recent prints is 0.2mm, so I set the initial height to 0.4mm. The Slic3r wiki talks about the benefits of a first layer of double the normal layer height and width with regards to adhesion. This has been borne out in my experience.
For my particular situation with the BuildTak and all, my z_offset worked out to be 0.015. I started at 0.1 and adjusted downward until my prints didn’t warp. Your mileage may vary, so you’ll have to experiment to get the optimum value for your setup.