2) typically faster than 20, perhaps 30-40 is a good start.
3) for PLA, you can get away with 40-60 °C easily. My Sigma has a glass bed that sits 3-4 mm above the heater pad (!) so my 70 °C setting results in 60 °C on the glass. I use glue stick. I recently learned of Elmer's PVA Glue Spray which goes on quite easily ( and bubbly ) but grips the part like it was all one piece! After a few prints, it releases more easily but those first few are knuckle-crackers.
4) I've been slicing with fan off for first layer, on for the rest. (PLA only, ABS is fan off all)

If you're getting a good base, the problem is either in the heater block getting too cold or the filament speed too high or the travel speed too high.
Have you checked the e-steps? Using a terminal program such as Pronterface, connect to the printer. Load filament and push a bit through to ensure that it's feeding well. Make a mark at the opening to the extruder or any convenient point, then make a mark at 100 mm from that point. When you command a 100 mm extrusion, the mark should move that precise amount.