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?
It's a blog. If your blog wins an audience, you gain influence. If you have influence over an audience, you have a captive market. If you have a captive market, you can try to sell them things or at least recommend things. If your captive audience regularly buys things, then you have a business.
Remember, all you have right now is an idea, not a plan. You need a plan that is structured enough to ensure you walk through each of the steps at the right time, understand your audience, and be patient enough to test as you continue to grow attention.
I'm very jaded about how easy some people think it is to develop an audience that will spend money because they are told to. It rarely happens. There are a few very visible people who have made this work, but even with a large audience, there is little security. Unless you are truly delivering something of value, your audience may raise your popularity for a while, and then drop you when they find another fad they like. Good luck. It's a lot of effort and doesn't happen quickly. Meanwhile you're not making money but being an influential blogger can easily be a full-time job.
You should position it as both. Go through a lot of Ecommerce websites especially in this industry and you will find that almost all of them have a "Blog" feature in the menu tab.
First thing you should focus on is starting a blog, creating content, and attracting an audience. From there you can begin to add items for sale our affiliate marketing products via Ecommerce to your audience. I wouldnt recommend starting with both at the same time. The blog is free and if you keep up with it it will attract viewers organically, to have your Ecommerce store work you will need to spend $$ on marketing/advertisement, people wont just naturally show up to your website right away.
The key here it to focus on 1 thing, remember, "If you chase two rabbits, you will not catch either one."
P.S Go listen to some of Scott Voelker Podcast episodes. He is right on the money and explains exactly how to do what you are interested in doing