I just do two sowings, one in late February with a bolt resistant variety like boltardy or pablo f1, plant out early april then I'll harvest them usually in early June through to july. Means i can follow them with something else like salads. They keep OK somewhere cool and I'll make pickle from them and use them fresh. Then I'll make another sowing in late june for autumn and winter beetroot. You can do any variety then and they stand frosts down to -3c or so without damage. They'll go mushy much lower than that though. But they do keep really well in my cold garage.
I'll sow them in modules inside, then put them in the greenhouse as seedlings. They survive frost well, but I'll hold back putting them in the greenhouse early march if there is a heavy frost forecast like this year we went down to -6c in mid march so I brought them back inside for that.