The description can be as long as you like, in one paragraph, so long as it's one idea. If there are two ideas, break into two paragraphs.
Dialogue typically gets it's own paragraph, even if it's by the character whose thinking generated the description that precedes it. Same reason. It's another idea, strictly speaking.
"Do you see what I mean?" GJ asks GI.
Who made this piece of junk? I can't ride it, he thinks. It'll fall apart underneath me. It reminded him of an old chair in the office which always fell into two pieces whenever anybody sat on it.
"Tell me more, please. About this ... thing, I mean."
"Of course, sir! It's a real treasure -- "
Don't tell me that! thinks he. I know what a real treasure this is.
The one exception is the case where thinking and dialogue, all by one character, are mixed together or alternate, if these sentences form a single idea. You could put it in a single paragraph, as is often done.
After some difficulty cutting the steak, almost instantly he regretted putting it into he mouth. "It's delicious," John mumbled to his grinning hosts. This chews like a rubber shoe he thinks. He bit down hard. "So how'd you make this? I mean ... it tastes great!" It tasted like the paper taken out of the office shredder, in fact. "Where did you buy this?" It's spoiled, they fed me rotten meat, thinks he.
John excused himself from the table after a few moments -- to go wash his hands. Actually he went to vomit. He thought he was going to die; he ran the entire way to the sink.