Installing CAN Bus I/O expander and wether to hardwire or use breakout connectors

I am installing a canchecked MCE 18 Canbus IO expander onto my 1996.5 Subaru Legacy Twin Turbo as I am installing a Link ECU into the car. The MCE18 came with a 34 PIN AMP super seal connector. I am a bit conflicted with how I should terminate the wiring from the added sensors to the motor and the added signal wires from inside the car. One plan I had was for every different set of inputs, CAN Bus, USB, IAT, ect, was to run a small jumper from the 34pin connector to a smaller connector as a breakout point. I will already be doing this for the extra I/O pins that I am not using. The other idea was to terminate everything straight to the 34 PIN connector from the harness I am making with the unused pins still going into their own connectors. Is there a standard for this or would it be up to me to decide? If so which way should I go? First time using one of these. Attached is some photos of the layout of the harness. For reference, the MCE 18 is going where the knockout is for where with wiper motor would've gone had the car been LHD.

https://imgur.com/a/M4WZkMp

There's not so much a standard as far as layout, I find the main thing to think about is how the loom will be installed and removed in future. Will it be easy enough to remove if the interior connections are wired directly to the MCE?

If you look at most factory harnesses, the engine loom to ecu is one main loom and then interior connections are terminated to a main connector. The interior connections are then branched off after this connector. This is mainly to make install and removal easier. Imagine pulling out your engine loom and you had to remove your dash and remove your entire dash loom too.

Looking at the layout you have, everything is focused in the engine bay, so it would make sense any smaller branch offs to the interior would go to a sub connector and sub harness that can easily be unplugged and run through the firewall. That sub connector before the firewall would have everything needed like CAN, USB, switch inputs etc from the interior and breakout after the firewall inside the cabin. You'd be able to pass through a single connector and branch from inside to the engine bay making it a lot easier to install and service in future.

On a side note, what extra sensors are you connecting? I only ask because I assume you are installing a Link plug and play, which has expansion connections that are generally enough to cover things like IAT, oil pressure, flex etc. You may be able to wire everything directly to the ECU and avoid an extra component and save some money. Again just asking out of curiosity and happy to help further if needed.

Thank you for the reply.

Should have mentioned that I put a Deutsch HDP connector set for my firewall "grommet". In theory as long as I unplug the harness from everything I could pull it out directly. In relation to why I used the can bus IO expander, this was mainly so I wouldn't have to go back in and pull the dash out to run more wires into the car. It would also allow for future sensors to be wired in more easily. There's also no really good spot to bring any more wires into the firewall as you have to deal with the intercooler and 2 turbos in the engine bay. It was a miracle I even got the HDP connector to fit where it did. The sensors I have installed are an IAT, combined pressure and temp sensor for oil, EGT probe at the primary (first) turbo. I'm also putting a provision in for a fuel pressure sensor to go to the I/O expander. The only sensor you can't run on can bus with a link is a flex fuel sensor so that one is being brought straight into the interior for when I install it in the future. Also, my plug and play ECU is missing some of the expansion auxiliary I/Os due to the fact it was factory modified to allow for full sequential twin turbo control. Trying to pioneer a solution for people in the future. If it would help, would you like me to draw up a diagram of where things are exactly going and what each branch is doing?