As a first machine I think the structure you have built looks fine, and will get you used to what CNC is all about. You will probably tinker with it and stiffen the gantry but the main thing is you will be learning and listening to the machine.

My first machine in around 2008(?) was made of plywood, with a Bosch router, 20mm un-supported round rails, 16mm ballscrews, 3Nm Nema 23 steppers, and a 24V all in one board (overdriven at 32V). I was not sure if this was a hobby for me, or if it was a passing phase, so went in with a minimum approach. I quickly found the shortcomings and went about upgrading.

Fast forward to 2021 and 4 machines later, plus lots of trigger's brooms in-between, I have a machine I'm finally happy with. The only parts I still have are the stepper motors and ballscrews !