If you could afford yourself the Rode Videomic Pro, why not go with a Zoom H1 + Rode Videomic GO and a Mini Boompole combo? In my country this combination would cost me only 30$ more than the Rode Videomic Pro and you would have everything except a longer cable (goes also for around 10$) to connect your mic on the boompole with the H1.
4K sure makes you future proof, but it still isn't necessary to my opinion if you don't need it for specific reasons. Even Full HD isn't the fully established standard yet as most of the broadcasts and films on TV only get delivered in HD.
If you think your camera is limiting you at the moment think about what you really need from a camera to work with it, e.g. ergonomics, ease of use, color depth, slow-motion etc. With these factors in mind sort out some options which are available.
If your current camera isn't limiting you in your creative ways then stick with it and maybe try to achieve the cinematic looks with lighting. There are still many great videos shot on Canons 600D and also on Nikons as you use.
Is the 5k budget only for the camera or does it also include the money for new lenses/adapters? Because a new camera system often goes along with new lenses and/or an adapter to make your lenses you already own suitable.
It would be helpful to now what you already have to give a detailed answer.
But if lenses and Adapters don't mather in your budget, I would take a look at the URSA Mini or the a7sII.
If you really think you wont need a zoom lens which covers the same focal lengths as your primes maybe also take a look at maybe the Canon 16-35mm 2.8 for wideangle shots or as Michael Tiemann already said in a telephoto zoom lens.
If you still consider the 24-105mm it is for run and gun a very good choice and gives you focal lengths from a decent wideangle to medium telephoto shot. As I use this lens myself very often, I have never experienced a huge drawback with the f4 in low light, especially if you own the C100 MKII.
By your statement that you don't need 4k in your case I would go for the cine-lenses with a Follow Focus or a good rig to use the camera in its best environment.
If you go with the XEEN-Lens option maybe also consider a good wideangle lens to go with the Steadycam which could be a other brand than XEEN because 14mm is already distorted on a Full Frame Camera. Around 16mm would be ideal to use on a Steadycam.
I would take a look at external recorders at a little bit higher price point (e.g. Zoom H4n is only 100$ more than H1) for the XLR inputs, because most higher-end mics (the Rode NTGs on which you are planning to use) have these connectors.
Best regards, Marc