Size of leadscrew clarification

I'm going to clarify my goals for a router table here...

The purpose of this router is to cut model aircraft parts in balsa in
plywood, with 3/32 and 1/8" thick being most common. Based on my limited
experience doing the same with a Fadal VMC, about 20-25 ipm is the most
pratical for the 1/8" bits I'm using (I could experiment some more
though, but I don't think it'll go over 50ipm tops). Rapid travel is not
a issue. Thicker material can be done in multi passes, but would be rare.
The maximum size is 12"x 48".
Using a trim router, with bushing to handle the smaller 1/8" bit.

The X axis would be supported on 3/4" or 1" hardened shafts, from
McMaster Carr. I would make some short rails to put under the shafts for
extra suport. The leadscrew would .200 pitch (5 turns per inch).
Y Axis would be 3/4" support shafts, and probably the same or smaller
diameter leadscrew as the X axis. The Z could have smaller shafts and
leadscrew, and would not need a backlash nut.

Note, I'm trying to do this as cheaply as possible, that means finding
the "unbuildable" components as inexpensively as possible. I can machine
most of the parts, but the Acme stuff is out. I would probably buy the
McMaster Carr 1018 leadscrews, but need to find the anti-backlash nuts
to fit these.

Other notes: accuracy of .005 is more than enough.

Other questions...can I use bronze bushing to ride on the shafts instead
of the platform blocks? I know they'd have to be open because of the
shaft supports, but thats not a problem.

Could a anti-backlash nut be made with Acme nuts and a spring, figuring
out some way to attach the whole shebang together?