Soak the soil well before sowing, cover with damp soil then drag dry soil over the top to reduce immediate evaporation.
Water down along side each drill/line of seeds on alternate days or every third day until germination, and then continue as necessary (unless it rains of course lol)
This works for me and have sown winter varieties of radish last week (now up)
Fennel might give you a small crop (mine have been in a few weeks now) and beetroot should give you something before the cold weather.
Chard yes (it is a beet really) but spinach is not yet imho as it hates the heat, unless you have virtually permanent shaded spot somewhere.
Spring onions I'd sow in modules in small pinches and plant out when they are well rooted, in a clumpr from each module