Vincent is not here-sorry.
I believe you have picked my brain before on other forums. Mine all ended up to be infertiles bought I can answer your questions based on what my female was choosing to do.
1) Substrate all three times. I provided multiple nest box and a large trash can and all were heated but she choose a decaying pile of mulch, leaves and dirt twice at a depth of 12in or so. She also laid in the dirt (after removing an nest box from location) that was near the basking spot and at a depth of 24-30in (freakin huge hole).
2)Mine seemed to lay 20-30 days after cycling (confrimed mating should be around the same time). Dave could shed some better light on that was suspect its close to the same for his lace monitors.
3)86 degrees fahrenheit. till eggs pruned. The norm for monitor eggs. High humidty and mid 80's will get you there. You will be waiting for a while. Large monitor eggs seemed to go 200 plus days before hatching.
Vincent is VaranusFricano from another forum you are already on
Other things I have noticed is food consumption is increase a lot. She will start to test dig a lot. Pay attention to what she seems to like. I would supply nest boxes and deep substrate. Each monitor is an individual so give her all the options you can at least for the first few times. Keep nest areas in mid 80's. Get the male out after the mating stops. She will start to become territorial. I have been chased out the cage by my female more then once after she laid.

I hope you get this