It will not be productive vs others, and cannot use modern carbide cutters, due to flex/vibration/chatter, effectively.
Your proposed solution will work fine at 5-10 ipm, feed,
This is 100% not true.
Do not listen to Hanermo, who tells everyone that they need to spend $20,000 on a 10,000 lb machine.
I built a machine 13 years ago, out of wood, using skate bearings on round pipe for the linear bearings. It still runs today, and I can cut at 200ipm, with carbide cutters. With better motors and drives, It could cut much faster.

Having said that, your design does have some serious flaws.

Not sure what material you plan on building from, but it looks like a simple aluminum tube?
If you want to use 80x160 for a gantry, it really needs to be a heavy extrusion, not just a tube. That tube you have modeled will easily flex and twist.

While skate bearings can be made to work, there are some things you need to be aware of.
They need to be in very tight contact with what they are riding on, in order to have a rigid structure. And on a flat surface like that, they are not very tolerant of dust and chips, and will bind if dust builds up under them.
You also are only showing bearings in one direction in each carriage. You need additional bearings to constrain the carriages in the other direction.

This is a very large machine. It's easy to build a fairly rigid small machine. But as the machine gets bigger, it gets much more difficult. Everything needs to be bigger and stronger, to achieve rigidity. And rigidity is of the utmost importance.
I think that you will be very disappointed if your first machine is this large. I would recommend building a much smaller machine, which will teach you where you need to improve your design. If you build something similar to what you've shown, it likely won't be worth upgrading in the future. Build a small, inexpensive machine to learn with, and a larger, more expensive machine when you can afford to.

You can not direct drive the pinion on the stepper shaft. you'll have poor resolution, and not enough power.