In your covert sub-d to poly option box raise the number from 1000 to say 3000 in your max base mesh option that should let you go from poly to sub d easier. Also in your covert sub-d to poly options make sure vertices is selected that should help your geometry stay clean.
Kurt
I am enough of an artist to draw freely upon my imagination, knowledge is limited, imagination encircles the world. (Albert Einstein)
https://www.artstation.com/kurtb