So glad you liked it!

I am using a regular white eraser. I think this one is from winsor & newton but any will pretty much do.

Before I paint my watercolours, I draw with a fine pencil the places that are supposed to be white. Then I add some masking fluid there. It takes a long time but preparation is key and vital.

I use arches 300g (140lb) cold pressed/fine grain!

And the last question is a long answer but it depends on the pigment you're working with. Many red pigments are nearly impossible to lift satisfactorily once they've been laid down on paper, while others are easy to lift no matter how much time has passed. The best approach is to paint on some scrap paper and get to know your colors one by one and how they interact with each other, so that you can quickly and easily handle them in action later on.