No, you also spend mass-̶t̶h̶e̶ c̶o̶s̶t̶ i̶s̶ t̶h̶e̶ s̶a̶m̶e̶ a̶s̶ i̶f̶ y̶o̶u̶ w̶e̶r̶e̶ b̶u̶i̶l̶d̶i̶n̶g̶ a̶ n̶e̶w̶ s̶h̶i̶e̶l̶d̶.-̶t̶h̶e̶ c̶o̶s̶t̶ i̶s̶ t̶h̶e̶ s̶a̶m̶e̶ a̶s̶ i̶f̶ y̶o̶u̶ w̶e̶r̶e̶ b̶u̶i̶l̶d̶i̶n̶g̶ a̶ n̶e̶w̶ s̶h̶i̶e̶l̶d̶.
No, it only repairs the shield while it is up-once it's depleted, you are wasting your bp as it does nothing.
It's related to question 1: the smaller the shield, the cheaper/faster it is to keep it up, but you risk a big shot taking it down before you can even start repairs or that it gets destroyed directly. Cybrans have both the cheapest and most expensive shields, which are generally considered the worst at arty wars if that's what you are asking-Seraphim's ones are instead arguably the best. Still, the ability to sequentially upgrade shields can be useful as it's a quick way to get a shield back up-Aeon used to have t2 shields that couldn't be upgraded (unless my memory fails me) b̶u̶t̶ t̶h̶a̶t̶ w̶a̶s̶ p̶a̶t̶c̶h̶e̶d̶ a̶s̶ a̶ b̶a̶l̶a̶n̶c̶e̶ d̶e̶c̶i̶s̶i̶o̶n̶.
