Created an account just to ask: why do you need 4K? Not disparaging it at all, in the market for a GH4 myself. But from everything you say it sounds like you need something else entirely.
Worried about needing new memory cards, new software, new computer. Barely any footage indoors. Fond of deep focus and small sensors. Sounds like you need something with internal ND and not in a DSLR form factor, like an HMC150 or AC160. Or a Sony RX10 might be a great middle ground. A built in ND, slightly smaller than m43 - 3x crop, servo zoom. Hell, what are you unhappy with about the D5300?
Again, I understand the temptation of 4K, but I don't understand why you would want it for your needs and with your concerns...