Hey, welcome!
If you already know HTML, CSS, PHP coding, you have tons of time. If not, you have a lot to learn, but enough time to do so assuming you put in the hours needed. IME this is a very common scenario: client presents an Adobe file and wants a WP theme just like it.
I advise that you not try to develop a custom theme from the ground up. You could find a theme that’s fairly close to the appearance and layout that’s needed. It could be further tweaked and customized to better fit the project at hand. A good way to customize an existing theme is by creating a child theme.
Seems simple enough, but TBH I’ve usually found that approach to be more trouble than it’s worth. There ends up being too many things to undo before you can do what you need. In practice I prefer to start with a basic starter theme like the one from underscores.me. It’s just a very basic theme framework. You’ll at least need to develop your own CSS to fit the project. It’s much easier to customize a basic front page template as you need from such a theme than it would be from a fully developed theme.
> I’ve been given an adobe illustrator file
This is for the design?
> and am wondering the best process and programs/ plugins to use.
The best plugins to use are the ones that fulfill your criteria.
Are there any functional website requests for anything other than a one-page website?
With hundreds of lessons to choose from, take the time to pick one and go for it:
https://www.wp101.com/#custom_html-17
https://www.linkedin.com/learning/wordpress-5-essential-training
Yes, you have loads of time.
