Screened soil - how fine?

Hi,

I'm looking to buy some bulk soil for my raised beds and I don't know how much screening is required to grow root vegetables and other veggies and it seems to have a big influence on the price.

How many kg should fill five 6ft x 4ft x 2ft high beds?

Should I be looking to make one bed acidic?

Also if anyone could recommend a nationwide or midlands supplier that would be great.

I want to grow sweetcorn, broccoli, cauliflower, parsnips, garlic, onions, beans, peas.

Thanks