Yes I think that its worth waiting, especially in view of the likely cool temperatures in early February. I have found that sowing onions that early is not always as successful as later sowing.
Moon dates are tricky, for example if you follow the constellations way of apportioning dates, there are root days on 8th-10th, and around new moon on 18th-19th. I think either can work for onions & beetroot, preferably if you can provide some warmth for germination.
