Converting a Sieg SX2P mini-mill to CNC

I am a complete beginner hobby machinist and would like to work with a CNC milling machine. Because of my budget limitations, I want to convert a Chinese mini-mill Sieg SX2P to CNC. I wish to cut mild steel with it, but mostly brass and aluminium. I read all of the available articles and sourced all of the 3D models, but I am still unsure of my conversion design.

The plan is to stiffen the machine as much as possible with the rear column stiffener and additional ground plate. I intend to fill all of the cavities with epoxy granite to minimize the vibrations. I also want to upgrade the spindle with a 1.5 kW (2hp) induction motor with variable frequency drive. The head will weigh about 30kg, therefore the Z-axis ballscrew is positioned directly through the centre of mass to minimise wear and side forces.

For the positioning, I intend to use closed-loop stepper motors and 10mm diameter and 2 mm lead ballscrews (from my amateur calculations, this should be enough, because the ballscrews are only tensily stressed with 5x safety factor).

The budget for the whole conversion is around 3000€ (3400$), maybe a bit more. Is there anyone who has already undergone a similar conversion and could help me with some feedback on my 3D model. Additional pictures are available in the Imgur album https://imgur.com/a/x2foxl6 I can also post the STEP file if anyone would like to take a closer look.

Thank you

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If you started with an SX3 you'd have a far more rigid machine to start with, probably a significantly stiffer column than your SX2 with the proposed tube & plate bolted to it.