It’s possible to build a multi-section online store using WordPress and WooCommerce but it does come with its complexities.
Having the three sections integrated within the same site can be advantageous in terms of shared traffic, cross-selling opportunities, and providing a diverse product/service mix to your visitors. However, this setup will be more complex and could potentially impact user experience if not handled correctly. You should consider separate stores if you expect substantial traffic or if the target audiences for the three sections are significantly different.
Here some tip that I can think of on top of my head:
Make each section of your site easily identifiable and accessible from the homepage and navigation menu. And each section will need its own SEO strategy. Use an SEO plugin like Yoast SEO to manage this.
You need to maintain a consistent design theme throughout the site for a seamless user experience. As you already pointed out, use plugins like WooCommerce for digital products, AliDropship Woo for dropshipping, and any reputable classifieds plugin for the advertisement section. The checkout process should be simple and seamless, regardless of which section a product comes from.
Also, I think it might be good if you will consult with a web development or eCommerce expert to ensure that your site’s architecture will be able to support your business model.
And there the links to the plugins I mentioned: WooCommerce, AliDropship Woo Plugin,
Yoast SEO. And if you’re looking for a form plugin, you can try Happyforms(which has a free and premium version). It has a payment feature so you can use it to sell products or collect payments.