Just briefly my two cents:
Journey is great, but also not that great. I wouldn't base my entire itinerary around it.
TDS is the park every fan wants and needs to see, but don't underestimate TDL. Amazing castle park. Do try to squeeze in as much of a second day as you can. I spend more time at TDL than TDS.
If you are still considering Nara, personally I think it well worth a day trip, or half day trip. It'll likely be easy to get too as well from your Osaka/Kyoto base. Don't wear your best shoes, you can't avoid the deer droppings.