Need some newie guidance on theme customization

Have a client interested in converting an established print newsletter to a ghost publication.

The general design will be pretty stripped down, without a lot of images other than some chart graphics, and the Journal theme seems about the right feel/structure. Have been playing around with it for a few days, and we like the functionality of the basic post and page editors, but I would like to be able to modify the look of the “home page” more that seems possible without modifying the theme files.

Things like enlarging the top section; adjusting some of the page elements; changing the wording on things like “next issue” to “next story” etc.

I am familiar with Wordpress, Squarespace and have a decent knowledge of CSS and HTML, but am by no means a developer. I can build sites in Wordpress and control most of what I need to with child themes or visual page builders, but neither of those seem to be a thing in Ghost.

I’ve made a few basic changes with Code Insertion, and I understand I can download a theme and modify it, and feel like I have enough coding experience to make some of the changes I’d like to in the files that way. But a little unclear what problems it will cause down the road with future updates if I I start making changes to the theme files, and what the recommended process for modifying themes is. I don’t understand Github or a lot of the developer lingo I am reading, though as I said, I could probably edit the files I need to make some of the minor changes we’d like, as I do child themes in Wordpress.

Anyway, and guidance for someone coming at this from my perspective would be greatly appreciated.

We may find we need to hire a developer to help or purchase a custom theme with more design options, but would first like to understand what changes we are capable of ourselves.