Addons are a known weak spot of the rules.
Pure or Open? - In the end this is each artists own decision. If you’d say that this is your own creation and only relying on external resources in a minor way, you should call it pure. Regarding the grass: I don’t think that using Grass Essentials gave you an unfair advantage, as the same result could easily have been achieved with standard hair particles and some green noise. So, if you don’t say otherwise, I’ll put this one into the pure category.
Good luck. Do you know what is causing the terrifyingly huge render times?
Textures aren’t mentioned in the rules specifically. Personally, (in most cases) I don’t consider textures a relevant factor regarding the pure/open classification. However, one could argue that they are part of the model. (Like meshes, particle systems, modifiers, …). As said above, you decide. As a rule of thumb: If you would feel bad if you won this round and called it pure, then you should probably switch to open.
(Mapping a photo of a carnival onto a plane and calling it a pure entry probably wouldn’t feel right. ;-))
That being said: A lot of things should be considered regarding textures. Pre-made ore new? Payed content or freely available? Who owns the textures? Are copyrights involved?..
Thanks Peetie! Usually I get away with ~3 lights. It is more like 8 this time. Not sure what went wrong here. 
Fascinating, never heard of that little boat. I’ve been to Newfoundland only once and I can’t remember seeing many rats - but you could actually be right. 