Oh, wow.
What would we do without the new fangled things in the world?
I have camped EVERY year of my life and here are some things I learned over the last 30 yrs... :-)
Tarps are a campers best friend. Put one UNDER the tent. Fold in the ends so that none of it sticks out from under the tent. Then put one OVER the tent and stake it so that it is not dumping water right at your tent... Try about 6 inches away. We always size our tarp to go to the ground on 3 sides and use expandable poles to hold up the 4 the side to make an awning. At night or on windy days you can tie the 4th side down and help keep the tarp from blowing off.
Rain flys are a scam....
NO CLOTH WILL BE TOTALLY WATERPROOF... Even treated.
If you trust that the "waterproof" cloth will hold up to a blowing rain you will get wet. It may work for a gentle short burst of rain... But not so much on the driving or prolonged rain. Your best bet is to tarp...
Buy the plastic stakes. They hold in the ground better than the metal ones that a toddler can pull out. One wind and bye bye tent....
Take a bathmat or door mat and put it right inside your tent door. Put the shoes on it IMMEDIATELY as you step in the door. A friend of ours in MO was camping and left their shoes outside... The 8 yr old found a black widow in his shoe. Thankfully he saw it and recognized it BEFORE putting his shoe on. (Yes, they put it in a jar and showed EVERYONE at the camp ground)
Good luck and I do hope that what ever you do keeps you dry... :-)