After creating design in Figma, can i replicate it through generated html and css in my Ghost website or there are some restrictions?
In its essence, all Ghost themes are just HTML, CSS, and some Javascript. If you manage to generate HTML and CSS from a Figma design, you will be able to create a Ghost theme from that.
Best to have a look here: Ghost Handlebars Themes - Building a custom Ghost theme - Docs
Here: Ghost Handlebars Theme Structure - Developer Documentation
And here: Ghost Handlebars Themes - Functional Helpers