Only problems I know of for the 104 are the wiring harness and head gasket.
Also the radiator if it has the plastic neck, and not the metal reinforced neck.
Evap core possibly, but if it isn't broken I don't see a reason to fix that until it does. unless it will cause other damage when happening.
Best thing to do is change the oil and filter every 3000 miles, use the right grade of oil for your climate and car, and chaneg it hot.
Keep it maintained.
You may want to have the suspension, engine mounts, trans mounts, subframe mounts, and all the other rubber suspension compoentns checked and refreshed as needed. This will help tighten up the ride. and smooth out the car. If it feels out of whack.
Have a full 4 wheel alignment done to factory specs. To help ensure proper tire wear.
Have the tranny fluid checked, and Get the fluid and filter changed if needed. Some will say not to do it to a tranny, so I say research if its ok or not. I would say its ok, but Others will say dont.
Other than that, Enjoy the car, they are great.
Send us some pics of yoru car, and post in the open discussion 300ce owners rolls call.
Welcome to the coupe club.