How come DPRK seems to have a copy of everything China has?
When you start studying them, you soon encounter a few interesting details:
1, despite the "evident" and ever-present expectations of China, there are very few Chinese connections. Chips (a way to slip by sanctions - and by no means the only one) and some heavy-duty carrier vehicles ... and that's most of it. Same with Russia(almost zero for many decades).
That North Korea does - it does either by itself (developing its own/self-obtained Soviet legacy), or with...
2, Iran. Iran can be found everywhere in DPRK military systems, and wise versa; moreover, it's to the point of visible cooperation and specialization of sorts. DPRK is tending to take more of heavy industry part of the spectrum, being much closer to an old-style industrial nation than Iran.
3, DPRK doesn't copy China all that much. What they do is they to their best ability counter/match(or overmatch where they can) ROK military in their eternal arms race. With....mixed results, but few nations do as well as them when economic disparity is this crushing - you have to give them that.
The same situation as with everyone - when they're sure what they're doing - they create their own systems. Where they aren't - they copy that works (recent totally not MQ-4/9 are a perfect example, copied to the last external curve).
Sometimes systems from both groups compete with each other.
4, With missiles/space specifically they simply aim for what they can - i.e. ground and sea-based deterrent, as well as tactical weapons.
No large surface vessels - it's utterly pointless, no big airspace - it's utterly unaffordable.
5, NK is quite capable in engineering terms. Ultimately, they have quite a lot of working development groups, supported by a significant education base.
Brain drain isn't a big problem for them(go try), there is a consistent state interest in explosive/flying stuff, and NK state can easily provide their engineers with conditions/prestige to make it a highly desirable career path. Prestige is a relative thing, after all, relative to people around.