I want to start a blog about interiors and home styling (high end) and then have an ecommerce store selling items mentioned in the blog. Later on, I want to have a sort of booking marketplace to book travel design experiences. 1. Is this a viable business idea? 2. Should I position it as a blog, an ecommerce site or travel?
I was going to say that I didn't find the idea interesting. But then, when I read Assaf's comment, and specifically when I have visited the provided example, of https://www.houzz.com, I was like "wow, interesting".
I wanted to start my answer with this duality to show a key challenge for you. That when you put the building blocks like you did, for example saying "a blog that sells items" you run the risk of others imagining things that can be very poor; and you could stumble in people that don't understand or think in something completely different from what you perhaps have envisioned.
Perhaps another way for you to explore your idea development phase is to ask less to others about your idea if the idea is defined in a limited fashion, like the above example.
And to move to the feedback collection phase when you have a more developed story. I recommend to you to consider tools like the Business Model Canvas but be careful to not fall in doing the process thinking that the doing of the process is actually working for you. Tools like the Business Model Canvas, or other process for design and discovery, are just lean-oriented tools — they don't move forward exactly, they are intended to learning with iteration model.
If you move forward with these lean methods, try to come up with a number of variations of business models for your ideas and remember that each of them are not final. For all models that you come up you may eventually pivot/change them as you iterate and learn, with feedback from experts-in-the-field, customers, etc.
I am pointing one direction, or thread, but keep in mind that this process involves lots of "triangulation" with other parallel studies. For example, studying the market, competition, trends etc.
One other thing to keep in mind is to go look for the customer needs — there are a number of Jobs-to-be-done articles and frameworks that are going to give you some rigor to keep the customer job/need story(ries) tied to your plan.
I covered some process to start moving but don't think that there is a formula here. Think that all lean methods for idea creation, discovery, and validation; are in fact learning iteration tools. Good luck.