With waist high weeds, you may have no choice but to mow the weeds.
If time allows, I prefer killing weeds to just mowing them. If possible, I would cut the weeds with a trimmer or brush cutter and then spray the entire plot with Roundup. Then wait a week and you can till or disc the soil.
Any ideas what you want to plant? IMO you are too late in the season for brassicas. Personally, I would plant a grain mix or a clover blend. Since you cannot control the weeds very much before planting, I’d consider this first crop an annual and plan on replanting next year when you can better control the weeds pre-palnting.
Grouse