Hi Trish. Although weather is mild in Malta, October/November are certainly the cooler months and off season. We visited in late September a couple of years ago and whilst the weather was warm, it was definitely not what I want as beaching weather. We adored Malta and are hoping to return early this September. You can comfortably 'do' it in two weeks.
Valetta is small by capital city standards, but lovely. Beware coastline to the north east of there as it is extremely commercial in many places.