That sounds like an ambitious plan. According to Wikipedia, the EU has about 13% of its external land borders fenced off, which amounts to about 1,535 km. The rest of the borders are either open or natural (such as rivers or mountains). Assuming you walk along all the fenced borders and ignore the rest, it would take you about 480 hours or 20 days of non-stop walking to complete your journey. This is based on the average walking speed of an adult, which is about 3 mph.

Of course, this is a very rough estimate and does not take into account factors such as terrain, weather, rest, food, water, visa requirements, border crossings, safety issues, etc. You would also need to plan your route carefully and avoid any areas that are restricted or dangerous.

As for how many walking shoes you should buy beforehand, that depends on the quality and durability of your shoes, as well as how often you change them. A pair of good walking shoes can last for about 300 to 500 miles before they need to be replaced. So, if you walk 1,535 km (about 954 miles), you would need at least two pairs of shoes, maybe more if you want to have some spare ones.

I hope this helps you with your planning. Please remember to consult a doctor before undertaking any strenuous physical activity and to follow the local laws and regulations of the countries you visit. Have a safe and enjoyable walk!
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