Mobile CSS to correct display errors

Testing on mobile, I have noticed the following display errors. Is there a CSS code you could give me to possibly fix these? 

Thank you in advance for your help! I have very basic WordPress knowledge & no development skills. Where to add custom CSS code in child theme?

1) Homepage (and other pages for main title) – The space between two lines of text (for the title) is reduced on mobile, hence the text look very jammed. Is there a way to increase the spacing between lines only on mobile?

2) Homepage – button on slider changes its size on mobile. Is there a way I can customize this? I would need a smaller button, about half the size as currently displayed.

3) Forums – Is there a way to customize the column length only for mobile, on the forum page? The first column is each forum name and description, which is about 1 third of the screen only, making it difficult to read a sentence (with 2/3 words on each line). I do not mind if the post count and the freshness of topics is not displayed on the forums landing page on mobile (if that can help gaining some space for title/description display)

4) Participate page – I have set my image carrousel with 3 images to display at a time (for desktop) Is there a way I can set to only 1 image for the screen width on mobile?

5) Homepage – slider. In slider settings, what is the ideal layer grid size for mobile, so my slide does not get cut (background image of slider is 1600 x 800 px)

Thanks!