Colin,
If it's like mine (see photo below):
1. Under the boom
2. It should have webbing straps each end to secure it to the main and mizzen masts. You could also try passing a line underneath the apex of the cover from mast to mast to get a nice horizontal ridge. Make sure that you have quite a high ridge (as in the photo), which gives you enough tension to allow water to run off down the sides without collecting anywhere on the way
3. N/A
4. Sprayhood down
5. Correct! But since the BR20 is self draining, it doesn't matter and keeping it open stops condensation. Mine survived head-on high winds and torrential rain in Pwllheli last year. Hardly any rainwater had collected in the sump, even though it had all its bungs closed (ie it was not self draining)
6/7. I start with the masts, work aftwards from side to side and then leave from the stern, which is more stable