Ultimately I want a PC controlling this stuff. I presume the decoder will report back via LocoNet. Is that correct?
If you use an Loconet enabled decoder Like the Digitrax DS64 then yes. A simple DCC decoder has only a one way communication.
However, I would also like to make a traditional display board with LED indicators as a project in the future. What are my options here? With my Peco points, I can at least add an accessory switch to do this ... what can I do about Tomix points though?
wit the Peco point you can feed back the actual position of the switch to the decoder and thus the loconet and your PC program. So you will detect if the turnout hasn't moved at all or even you will detect when a turnout has been operated manually. Thats what the real railways do. Unfortunately Kato and Tomix switches do not have a feedback switch built in.
There we have at least two possible workarounds:
1: Use power routing and detect the power and feed the information back. That will use an optocoupler a quite cheap IC
2: Disable power routing and rewire the built in switch in the turnout as a feedback switch.
To built a panel there are several Loconet I/O modules on the market. you even could use a DS64 to dive your panel indicators. Although thats not very cost effective.
Finally, I just don't get the routing features at all. I downloaded the manual and read through it ... maybe it is something I need to play with to understand.
If you want to use a PC to control the routes you will not need that feature. Basically you push one button and several turnouts or other function will switch. You don't need to understand it. Its just a freebie feature.