Being in the US, I can’t help you much with series anywhere else, but I can help with engines! Currently I run a Rotax Sr. Engine, one of the most competative engines in just about any class. I know that Rotax have their own series in many countries, but if not, this engine has a lot of torque (Good out of corners), while not losing to much in the top end (Top Speed). There are other engines too (IAME Parilla is another competative engine, however it is very different from the rotax; high-revving-top-speed engines with relatively weak bottom end rev range, good on high speed tracks). And if you want to get into it even more proffesionally, Rotax has a very well structured system of championships, which makes it easy to compete in.
Hope you get into it, Karting is one of the funnest things with four wheels, while still not being incredibly expensive. That being said, if you want to be competative, be prepared to spend some money. Here in the US, some well funded drivers spend upwards of 100,000$; some spend much more. Of course, that doesn’t mean its imposible to be fast while not spending that much, but those drivers have a bit of an advantage due to the almost limitless resources….