Boers won their first battles against red-coats because they refused to wear red coats, stand upright or fight in lines. Instead, Boers used the newest and best Mauser bolt-action rifles combined with ancient hunting techniques to kill hundreds of British soldiers. Boers won their first few battles because they fought smarter than European soldiers. It also helped that Boer farmers' clothing blurred into the local shrubbery when they lay down to shoot. Most people shoot more accurately when laying down. Boers also had a far better understanding of local shrubbery.
Which was possible because they UNDERSTOOD both the trechnology and tactics they, and British, used, and were able to counter it. Without such understanding, the countering would be impossible. Before the era of rapid firing rifles, the scattered formation would be essentially suicidal; the enemy line infantry would just broke it by bayonet charge (like British army repeatedly crushed minuteman militia during Revolutionary War - minuteman could shoot, but have zero standing power).
Is there anything preventing Dutch ships from visiting Zenland to sell the latest in European industrial products?
Industrial products by themselves is not enough. You could buy European rifles, but not understanding of European tactics and strategy. To achieve that, you need to make your brains working like Europeans; to westernize, to refit your culture to most modern standards. See the historical examples; Pyotr I rebuild of Russian Tsardom into Russian Empire, and Meiji revolution/restoration in Japan. In both cases, the "native" culture were quite roughly bend to accomodate European thinking.
Zenland only buys handfuls of European weapons, but prefers to build them under license.
It requires a very developed industry. Do not forget, that even Japan, starting the massive modernization in 1860s, was forced to fought Sino-Japanese and Russo-Japanese War, relying on foreign-build warships. The modern rifles are quite hard to produce for not-exactly-well industrialized nation.
Is there anything preventing Zenland students from attending the better engineering universities and medical schools in Europe?
Society and traditions. Also money. But mainly society. The need to send Zenland students to Europe must be REALIZED by local elites; they must realize, that their age-old traditions and cultural customs worth little now. And not only elite must realize it. The average Zenlanders must be "programmed" into thinking
"modern, foreign - good", for modernization to sucseed. Otherwise it would be a classic problem of semi-modernization; a small, Westernized elite, ruling over traditional population, which view elite with contempt for "straying out of traditions and culture".
You see, I pondered quite a lot about the modernization of traditional cultures. It is not exactly easy to achieve. A lot of factors must combine to make efficient modernization - like Russia and Japan - possible. Otherwise, you would have half-hearthed semi-modernization, like in Imperial China or Ottoman Empire, where a lot of efforts were spent on adopting external appearance on modernization (like buying modern arms), but little was done to change the culture and state structure.