2. confirmation speed as above posted mentioned is determined by the time between blocks. and that time is a somewhat fixed time. bitcoin is designed in a way to have 2016 blocks every 2 weeks which translates to 1 block every 10 minutes. this doesn't change with more or less miners. when the number of miners (or more accurately the hashing power) changes there is thing thing called "difficulty" that changes so that we get the same 2016 blocks every 2 weeks again.
Imagine the queues in the shops if Visa batched their transactions up and authorised your payments in 10 mins blocks. That is probably the main reason Btc hasn't (and probably wont) taken off. People just don't want to wait. Even if they halved it and halved it again, that would still be 2.5 mins waiting for payment to clear. The lightning Network is ok but if your main selling point is something that just bypasses the main protocol, then why bother with the main protocol.