Broccoli, baby leeks, spinach query

Last year was my first growing veg, I grew peas and beans. This year that same bed has good soil as I had added a little compost. I now have two more beds available, and I want to grow Broccoli - Sun king F1, baby leeks, spinach perpetual.

Both these two new beds have extremely heavy clay soil that I feel is a waste of time growing directly in it, and I have left it too late to improve the soil.

Which plants would be best planted in last year's bed with good soil, and can I plant the other two beds with the seedlings in plastic pots with potting compost? What depth of pot should I use?

Thanks