1) No, PSoC5LP will not behave differently when Device Power is set to "Self Powered" and when it is set to "Bus Powered". The change will only be in the descriptor that is being sent to the host.
2) The following table give gives the range of voltage that should be supplied to the USB block. When the supplied voltage will be within the given range the VBUS detect should be high. The threshold value will be same as that of a SIO pin. Please refer to the PSoC 5LP datasheet ' SIO DC Specification' section for the value.
I am check for points 3 and 4 and get back to you.
Do you have any update for points 3 and 4.