why not just get a kit ?
Have a look at the folgertech ft5 - fits all your requirements, full kit runs at around $499
https://folgertech.com/products/folg...3d-printer-kit
300x300x400 print volume.
All metal cage construction - so very easy to enclose.


The other option and another $200 but with larger build volume is a delta kit:
The he 3d kt280 $560 (with store discount) https://www.3dprintersonlinestore.co...3d-printer-kit
280mm base by 600mm build height.
The kt200 - same kit - but around $199 and 200 x 300 build.

If nothing else, looking at the build videos will show you what bits you need to source to build a machine from scratch.