Must be laid in one continuous lay or you will end up with joints that could potentially allow water to pocket. If this freezes, it will lift the surface. Personally I would leave it to the pro's. Resin looks great when done right but an expensive mistake when not. Nothing to stop you doping all...
Never permanantly get rid of them unless you remove the ability for them to root. Filling the gully with something like 20-40mm Pebbles will still allow drainage but won't give the weeds a medium to root in.
The Type 1 in the white box is how it should be, 40mm down to dust. The area to the right of the box shows materials without enough fines in. It looks like a rake may have been used to level which has left the fines behind. A board rake or back of shovel should be used when levelling type 1 so...
If there is no sub base such as Type 1 then yes, use a membrane. If there is a sub base the membrane should go under the sub base and not between the sub base and finished gravel surface.
We use it a lot. As long as you follow the laying instructions and have a good free draining base, it won't give you much trouble. There is a good variety around now also. We tend to use Cotswold Self Binding Gravel which is quite a bit cheaper than Breedon.
We purchased one during lockdown. I was totally against it to start with but to be fair I'm in it the most these days. Very expensive to run in the winter but IMHO, worth it.
The sub base is fine there's just nothing holding it in preventing lateral movement. Sub base appears to be above ground rather than below it which is the issue. Concrete doesn't look like it has been pokered very well though.
You must absolutely keep 150mm between finished level and DPC. Water will breach your DPC otherwise and cause damp issues inside, not to mention green walls on the outside. Also, if you try to sell your house it will show on a survey. If you need to gain more of a gradient for drainage you can...
I understand where you are coming from but It's going to cost you more in the long run when you have to do it twice. Plus you will have twice as much waste to get rid of if the lean mix fails