New Field- New to Veg Growing - Raised Bed Help Please

Hello I am a newbie here and also new to growing my own. The only gardening experience I have is 6 years of growing flowers from seed for a small container garden in the yard. In September last year a friend offered me the use of a 70ft by 50ft field that had not been touched for 30 years. Anything I do has to be organic.

The field is very heavy clay and was full of Brambles, nettles and thousands of 6 foot tall Rosebay willow herbs and couch grass. We set about digging out the weeds, it was a complete mat of weed roots and the Rosebay Willow Herb roots go down 3 feet in places. Still digging them out

My original intention was to create an edible garden with vegetables planted with flowers in the ground and not the typical allotment look but with the ground being so heavy with weeds and every missed bit of root growing again I think I many have to go the raised bed route unless someone has some magic tips for me?

I have 2 metal raised beds to go in and have read so much I am tieing myself in knots about the best soil to fill them with. I have some bulk bags of compost ordered. Can I use some of the existing clay soil in the beds if I am careful to remove all the roots I can see or do I need to buy some topsoil or specialist veg soil? Any help and advice would be greatly appreciated, and sorry if it a dumb question, just want to get it right as I am on a small budget.

If you are doing raised bed no dig there is, in my opinion, only one place to go... youtube and search out Charles Dowding. He has a huge wealth of knowledge and his videos are very educational. If you subscribe to his channel you can then follow all his new videos. I would also advise maybe sending him an email explaining your situation. He is very helpful and will give you good advice. On the perennial weeds. If you hack them back to the ground although you could remove such things as bramble, what you can do is cover the ground with a few layers of cardboard to suppress the weeds and then cover with a thick layer of compost and plant into the compost. First stop is to check out what he does here. I do no dig following his methods and I like the results one thing about no dig is that is does require a lot of compost for topping the beds. I have bee using a lot of farmyard manure this year because I can get it for nothing but I am expecting that doing this can have an effect on the soil chemistry so will maybe have to add lime. I really don't know opinion seems to be divided as to the actual effect of adding well rotted manure to garden soil. there is a link to a video below which will give you some idea of what is involved. Good luck!

Start Out No Dig, one method with cardboard and compost - YouTube

Thank you very much wolveryeti and jambop for the advice, I think my problem is that I have read so much conflicting advice that I did not know where to start. I am leveling the top of the field into a terrace as it is quite a steep slope before putting in the raised beds I have. I will give your method a go on that wolveryeti and use some of the existing clay in the bottom, they are quite deep. I am not in a rush but would like to get some veg going in June, having something growing will help me keep going. I am planning on trying the no dig method jambop and have emailed Charles Dowding for some advice thanks. I will have to experiment and see what works best in my situation. I am feeling a bit daunted and think I should have started on clearing a smaller section rather than trying to attack the plot as a whole. I have some weed membrane and planning on getting more to cover the open ground until I can tackle it.  Thanks again to both of you for your help.