aha I've just found your first question.
For the weeds and rubble - no easy answer there, just plenty of elbow grease, and a skip, or drive the stuff to the tip. Put good thick gloves on and dig the whole lot out. Some persistent weeds will come back, you have to keep at it before you've won. It's up to you whether you go down the route of using weedkiller (i would not personally) as that will mean there is a delay before you can replant with something more attractive.
What kind of plants do you like, and how much light does the bank get?
You can have a search around the GOY site and get some good ideas...
maybe look for how other people have done their planting on a slope or bank

You can also do a search for what will be good to look at in September in the UK - maybe asters (Michaelmas daisies)? Sedums are also a useful late-season-interest plant.
Good luck anyway!

Try not to let the weeds get too rampant before you get a good layer of soil on it..Keep the Round Up going while you get some ideas. It would look lovely with lots of naturalised bulbs ( time of year for that not now) Grass it over. I have a relative with a similar bank outside their garden but on their land. They got it professionally done over and it is still weedy and unsightly. I saw a bank near a canal lock with massed cowslips, really fantastic. Sorry first post while I was typing in. I was trying to make life easy for you, and simpler based on coping with the most rubbish strewn garden you ever saw. We buried most of it with a shared bulldozer (down deep) right in the middle of the garden.

Yes cowslips next Spring will look great. You can plant seeds in the autumn, I have spare seeds if you like?