Splash page to different site sections

Thanks for any help you can provide me with. I’m fairly new to WordPress and am trying to pick my way through some site customization for my design business so that I can avoid having to hire someone. I’m getting fairly proficient with working within themes and templates, but I’ve hit a bit of a wall.

I’d like to change the setup of my current homepage, https://www.cyanotype.ca
Right now I have one single-page site up there. I’d like to change it so that when you go to the domain, you get to a splash page that simply has my logo, and two buttons – one button will say “Book Design” and will take you to the current website, exactly as it is.

The second button will say “Full-service graphic design” and will take you to a site that is exactly the same as the current book design site (same theme, etc.) but will be different portfolio items.

Any thoughts or suggestions on how I’d set this up with subdomains, splash page plugins, etc? I’m afraid of playing too much as this site took me some time to put together and I’m worried I’ll do something stupid.