I think the size is fine...I am a home player...18: deep is not that much...take a measure tape & pull it to 18:...not that bad.

As to Korg vs Yamaha....I know its conversed all the time...but for the music I like and play...the Yamaha has sounds and styles that fit that music much better.
BUT, the last Korg I had was PA2XPRO. It had a lot of poor quality sound issues...if they fixed them all...then well OK.

I have always thought Yamaha arrangers have a nice sweet sound...Just saying....IMHO