Used panels aren’t difficult to find. Last I looked they were typically around the $ .20/watt range.
I used gogreensolar for a new diy project. Make sure you understand your interconnection process. If you turn on before the meter is changed you may be paying for electricity out as well as in...
In order to use 0-10 you will need dimmer switches designed for it. Usually these are part of a system with occupancy sensors but can be standalone. They also require 2 16g wires to control dimming. More of a commercial setup but they are better than residential dimmers.