When I use a standard stock tank for a brooder, I heat it to 90F on one side the first week, and decrease by 5 for each week of age. But I do notice that my room temps may cause the brooder temp to fluctuate a little between night and day. As long as they have a cool end to go to, that is good. The leg issues might get better with riboflavin (vitamin B2) which is in some chicken vitamins and vitamin B complex tablets (not B12.) Some also use baby vitamins Polyvisol without Iron 2-3 drops orally each day for the ones with leg issues. Chicks with pasty butt issues should be checked daily for recurrence until they are 10 days old. Sorry that you have lost some, but hopefully there will be no more lost.