I'd second what @murphaph and @Irishswissernie say.
Starting online to test the water before opening a physical shop is a no-brainer.
I'm sure that there are rules of thumb as to how many years of losses it takes in various industries before breaking even, so you'd need to look into that.
If it's five years and €500k invested before you break even, for example, you'd need to have that time and capital to spare, while also having means to survive personally.
You'd also have to ask yourself why people would shop with you over the competition.
Why would a customer of Marks Models for the last twenty or thirty years drop them to shop with you?
What are you going to offer that is so much better?
Marks Models website is rubbish compared to Hattons, so having a decent website that is updated daily would certainly be a good reason.
Ditto the search facility.
Search for something on Marks Models website and you get no images, no alternatives, just a list of text-only entries.
The easier it is to buy from you compared to your competition, the more likely that people will spend more, and will return.
A well laid out website, a great search engine, regular updates, clear and accurate photos and descriptions, and you are certainly part way towards success.
An example of another great online shop is the IRM store.
It's so well laid-out that you don't even need a search tool, but there is one, and it is excellent.
Either way, best of luck with the venture!