Not sure why you want a step up. That's just a trip hazard waiting to happen. Keep it all one level. 10 feet is plenty hight and it is perfectly normal to have the entire home one height.

I'd keep the floors and ceiling all at one level. Saves worry about falls, or about people who have difficulty managing stairs at all. And, while I don't like to use the word "dated," bilevel living/dining areas strike me as exactly that.

No step would be my choice but I also think 10’ ceilings gobble up heating and cooling for no real purpose, I think in the near future those heating and cooling bills will be big issue for all of us.

I wouldn’t do a step up either.

Addressing Patricia’s comment; look into radiant heat instead of the typical hot air or baseboard. I had it in my last house with cathedral ceilings and it was fantastic. The system ran off the gas furnace and the floors and furniture were never cold. My gas bill was very affordable because of it.

"Doesn't a dining room come higher ceiling?"

Whatever does that mean?