Used to is past tense so we can say pehle
You can add पहले but it is not required. 'सोते थे' is in the past imperfect tense (which is absent in English) and conveys the same thing as 'used to sleep'.
Thanks for mentioning it. This info that it is called "past imperfect tense" and lack of it in english thereof is the info that bugged for me quite some time.
U r Absolutely correct
Not mandatory or necessary.
Yeah you are right
"Thin mein ve sothe the" is this wrong?