Texturing various questions questions - Cycles I was wondering various things while I was following several tutorials on the topic, which in the tutorial (timelapse unfortunately) I can not understand or even from my render.

1. In the picture I textured the wooden planks but they are two different parts (I have highlighted them below), but there is that ugly effect because the textures do not match. Does this defect have a name? I think so but I do not remember ... more to have to fix it not only there but for the whole structure it takes a lot of time, can I do that or I'm doing something wrong? I was thinking of removing the various vertical edges that divide the wooden boards, but some polygons would remain with 5 vertices ...

2. to make the brick wall I did various tests, in the photo is just a flat wall with the texture above, but I had tried with various combos (subsS + decimate + same texture in black and white) and gave a nice effect but I was going to fill the structure with too many faces / polygons. do you usually do that or can you use some trick?

3. Finally, I noticed that after having texturized an object if it is already texturized, with knots and applied materials, it is advisable to save time creating the different assets (in my case it is a mediaeval house full of wooden beams) ) and repeat them to save time?

thank you and sorry if I have dwelt, if I have not explained well please tell me.
1) The term you are thinking of is "texture seam". Generally, if you have one flat side of an object, you would try to unwrap and texture it to avoid seams. it might be that the texture you are using isn't suited to what you have. 

2) I quite favor using micro-displacement for close-up images that require a lot of detail. However, if you are not going to be quite close to your object, it is possibly better for you to use normal/bump mapping. It is far less computer intensive than displacement/subdivision.

3) Yes, you can reuse assets and textures. Taking your wooden beam example, you might find that creating only three different beams, and using these in your scene gives enough variation. There is a trade-off between saving time/effort and avoiding repetitive items and textures.