Are a hyphen and capital needed?

Anwar was first tried on corruption charges and then for sodomy after his sacking as deputy prime minister in 1998 amid a political feud with then Malaysian premier Mahathir Mohamad.

His sodomy conviction was overturned in 2004, freeing him from a six-year prison sentence to lead a three-party opposition alliance that staged its biggest electoral success in 2008.

1. Should there be a hyphen after 'then'?
2. Should 'premier' be capitalised?
3. Is the part in bold correct? Shouldn't it be replaced by "sentence, which allowed him to lead..."

Thanks in advance.