I haven't done anything with z-offset, but is that any different than just tightening the leveling screws? I found with glass that I need the nozzle to scratch a divot into a post-it note held on the glass to be close enough to stick at all. Any looser or tighter and it wouldn't stick, it would usually curl up and get stuck to the nozzle and then there is no hope. This is definitely closer to the bed surface than with the Creality build-tak surface. I usually print with the default Cura Ender-3 profile which is at 50mm/s and 50% so 25mm/s for the first layer, should I try even slower than that?