I will focus on buffered two lanes according to what you recommend. My trains are: <C, <C<, <CC<, <CCCC< (with C: car and <: locomotive with direction).The intersections in the OP are solid. However there are intersections with higher throughput. I have posted multiple in this forum.
Depending on how long your trains are and how much ressources you plan to put on trains you might not need high throughput intersections.
Most intersections in your base should be basic ones, but areas with high loads need high throughput intersections.
If you want a type of highway you might want to make highway rules. Like all intersections on a highway are high throughput ones and you try to merge as many lanes as reasonable possible before they get to enter the highway.
Regarding 4 lanes.
2 lanes with high throughput intersections has a really high throughput, about 33 per lane with 2-6, while 4 lane with no buffer intersections with many crossing gets about 7 trains per min per lane.
Unless you have really long trains I would recommend 2 lanes with buffered intersections over 4 lanes with unbuffered intersections.
I like to test things myself that's why I tried to use your intersection test bench but I failed to make it works. I found the command panel and try to launch train but they are all stuck "no path".
Are some mods needed and I missed it (in this case sorry) ? Thanks
Edit: Installing Creative mod and Automatic Train Development fix the problem
Edit2: Should I choose EQUAL or PLANNED Right Hand Drive ?