Exactly, all the "live" this and "cycle" that...
The quesion is, do you have enough bacteria to eat the fsh waste?
Are you losing some with the sand being lost/washed? Yes. Most likely it will not affect the levels all that much when you are increasing water volume by four.
"Live sand" also has worms, bugs and other critters. That's why I say save some. What you don't want is the sulphur and malm that collect at the bottom of the sand bed. The sand itself is pretty negligable. New, old. Doesn't matter. I have 5 fish in a 125. How much bioload is that? Nothing, compaired to 3 in a 33 solana. Stop overthinking it.