I’m a multi-year MOCA user, your use case seems appropriate. I actually have two sets of adapters in use in my home network in rooms with (inexplicably) only coax lines run. I’ve had great luck with mine, they are as fast as I need them to be for gaming, video etc. and have been extremely reliable.
I think your description makes sense on setup, I don’t have cable modem so I didn’t have that, but it should basically be:
- Ethernet from router to MOCA adapter A
- Coax connection from MOCA A to destination room
- Wall coax to a splitter - it should be MOCA compatible (assuming you need tv and internet) 3a. Coax from splitter to TV (assuming you need it) 3b. Coax from splitter to MOCA adapter B
- Ethernet from MOCA B to device. I actually got a small 4-port dumb switch as an Ethernet splitter just in case I wanted to plug in multiple devices.
I’d recommend getting MOCA working without the splitter first and then once you confirm, then add the splitter, it will be easier to troubleshoot if something is working. Good luck!