Thank you Rai, problems 1 and 2 are solved now, what a relief!
About number 3, they say some parts of the sidebar, like p.e. instagram picture overlaps the posts in mobile view, i don’t know which model or browser they use, it happens only to a couple of readers :S
I’ll try to solve number 4 with your recommendation, but I have another question about this, Related Posts showed are the lasts of the same category that the post, right? not necessarely related in content.