No, it is fine to use a coupler.
If it is outdoors, please make sure that you fully weatherproof the connection.
Water ingress to the RJ45 connectors and corrosion of the sprung copper fingers within is still a big cause of camera failures.
Motion detection can be problematic - as any change in pixels in the scene/detection area may trigger it.
It is therefore very hard to optimise it for all conditions.
Many people switch to line crossing detection; simpler and more reliable.
Enabling h.265+ does use up some of the camera's...
It is very likely that you have just not configured Hik-Connect properly.
You need an account at www.hik-connect.com
Add your NVR to that Account.
Install the Hik-Connect App on your mobile phone.
Login to the App with the same credentials that you use for your account at www.hik-connect.com
My preferred route would be to use a software on a server solution such as Luxriot.
And use capture cards to connect your existing analogue cameras.
We have done this previously with casinos with high camera counts.
Stand-alone encoders, to convert analogue to IP, are expensive.