Faraaidh and Sunnats of ghusal

Q: Can a person gargle and make istinshaaq before sehri ends and thereafter make ghusal? 

Q: Can a person face his back towards the Qiblah while bathing?

Q: If I do istinja in my shower with the water from my shower, will the floor in my shower become najis? If it becomes najis, how can I purify it?

Q: Which direction should we face while taking bath?

Q: On average how many minutes should a:

1. Fard ghusal take?

2. Sunnat ghusal take?

And how should we get rid of doubts when taking a ghusal?

Q: When a woman who has plaits performs ghusl, is it compulsory for her to wash the entire length of her plaits or is it only compulsory for her to wash the very bottom of the hairs which are plaited.

Q: When performing ghusl, is it compulsory to remove all the mucus which includes dry mucus and wet mucus which is inside the nose?

Q: I have read somewhere that while making ghusal, if any part of our body gets dry before purifying the other part, I have to repeat my whole ghusal (i.e. suppose if the water output of the tap is too slow and after washing my head, when I reach to clean my legs, some parts of my head or arms had already dried, do I need to repeat the ghusal? 

Q: Can I use that water for ghusal which I have kept in a bucket for ghusal, but while making ghusal, if the water droplets from my body falls into that bucket where I have kept the rest of my water, is that water pure enough to make the rest of the ghusal?

Q: I recently got my braces off and there is still some glue from it stuck on my teeth. This is normal because the glue is transparent and may be difficult for the dentist to see. However, my next dentist appointment is next week and this week I will have to do ghusl after my haidh ends.

I can’t get an earlier appointment. When I looked online for solutions to get the glue off, they recommended stuff like baking soda but these things can damage the enamel. Will my ghusl be valid with this glue on my teeth?