well, improving support of dimensioning is now in progress, and I suppose in nearest 2-3 weeks there will be release where it will be extended.
As for your questions:
1) please check Drawing Preferences -> Dimensions tab, there are setting that controls dimensions rendering.
2) mmm... that's strange. For linear dimensions, there should be 4 points - 2 definitions points (where extension line starts), definition point and text mid point. Please select dimension object and check again.
In 2.2.2 alpha branch, it is possible to increase the size of the grip point via settings (
https://github.com/LibreCAD/LibreCAD/releases/tag/2.2.2_alpha-latest).
3) actually, as for 0 layer - at least in LibreCAD, there are no technical limitations that prevents you to keep your objects in that layer (yet you can't delete layer 0).
If you create blocks - it's better to keep objects for the block within layer 0.