I'll post mu 2Cents.
I did not want to spend a ton of $ on a rig that I wanted to keep minimalist.
Before you do any audio work on a diesel, you need to do some sound deadening or you are wasting your time. I used Kilmat and marine carpeting paying extra attention to the dog house where most of the sound and heat comes from. Several threads on this topic.
Next I did have a radio shelf in the rig so I built the system on top of that.
To keep costs down I used a Chinesium headunit. There are many. They are about half the cost of mainstream brands like Kenwood, etc. They all have major weaknesses so research them carefully do you don't get one that will not meet your objectives. Some really suck.
For me, I wanted want that would connect via Android Auto flawlessly, and had low energy BT capability that I could use for TPMS, and had the largest screen I could get to run Waze and my streaming app together. I ended up with one that had a 15.1" screen.
For speakers, since I have a Helmet Top, I just got a cheap set of used weather proof speakers and a cheapie chinesium subwoofer with an integrated amp.
Not a Symphony experience, but better than nothing.