Multiple issues with JustWrite theme

I’m using the JustWrite theme and have multiple issues of concern which I’ve tried to address using plugins, which have not worked at all. Any thoughts much appreciated as I’m tearing my hair out..

1) Home page excerpts – More tag doesn’t work, just creates a gap on the full post page and doesn’t show on the home page at all. I also want to be able to remove/alter part of the excerpt that is being pulled in – a credit to where my work originally appeared, which is in a separate paragraph and in red on the post itself, but is just running into the first paragraph in the excerpt.

2) I can’t adjust featured image size, I’ve used Regenerate Thumbnails which the theme documentation tells me to, and it does show the featured image adjusted in the post editing page but doesn’t actually make the change on the site

3) The images in the featured posts in the slider are cropped a different size still and look strange – I can’t see how to alter this.

It may be that all this could be fixed by editing the CSS stylesheet, but it won’t let me – when I go into the “edit css” window, there are instructions to remove the comments and paste my edited code, but when I do that and try to save, it just reverts to the instructions. JustWrite does say that editing needs a child theme but also that you can change in the edit css window. Do I need a child theme? I am fairly new to this and not sure how to even start with that.

Any help much appreciated!