sounds like he wants to use ready rod
your motors will twist the screw into a pretzel , i have stainless screws , the one end was turned down to 3/8" . the x axis with a 1145 oz motor eventually twisted and broke the 3/8 dia , that was only a 1.5" length that was 3/8 on the 3/4" screw.
over the distance you have, you will destroy those screws in no time
if you going to use a cheaper type of leadscrew i would suggest using a 3/4-6 acme which is my preference diameter or a lot of guys are using 1/2-10 4 start acme
A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........