It's perhaps unrealistic to expect the forum to staff your project, your boss or peers should be providing primary support / direction on your project, or consultants your company engages.
As Pavel indicates Linux is free, but all the support burden fall on you. Unless you've got the staff to support development best to stick to reference designs, or those with an already large/heavy project support community around them, beyond the vendor. The vendor's priorities are not aligned with yours, and they can/will change direction when it suits THEM.
It's not the physical size of the screen that's the issue with these MCU/MPU, it's the resolution. The 2-Lane DSI is perhaps limited to around 1388x768 RESOLUTION. If you need something more capable, you'd be better suited looking to solutions tailored for the Tablet market. Large screens want wide memory interfaces, so high pin count devices. BGA's are unworkable for many due to the density, ball escape, and lack of probe-ability / rework.
Most ST boards come with schematics, gerbers, etc under the "CAD Resources" tab, these will use products ST choses, you'll have to import/export into whatever tools you choose to use.
How much RAM and processor resources do you actually need? The human body is relatively slow compared to those of an oscilloscope, or software-defined-radio application. Do you need more than 256MB of RAM? Code beyond 256MB, storage beyond a few dozen GB ?
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