Regarding your first question, you just need to make your road mesh has a tiling texture, then for each mesh you spawn using the L-system make a Material Instance Dynamic and then set the scalar parameter for tiling to match the length parameter from your l-system.
fwiw I have made a whole L-system using blueprints a year ago or so. I am about ~80% though rewriting it in C++ because blueprint l-systems were too slow. But I did manage to program most of the core l-system features into blueprints such as parametric variables and variable checks. I was planning to release it at some point but I keep getting wrapped up in other deadlines. I’d be happy to post some examples of how certain bits work if that is helpful.