Joying RK3188 questions

Hi I have a Joying RK3188 and I'm wondering a few things before I install a custom ROM. First, if I do a custom ROM and MCU will I lose the phone mirroring? I've heard/read different opinions on this and it's a great feature that I do not really want to lose. Second, has anyone tried using it with a AT&T Mobley? Does it maintain the wifi connection? Third, does using a custom ROM allow me to set the power off time to something > 2 hours? I've read that the energy use is minor and that 24 to 48 hours should be fine without killing a battery. Finally, what's the difference between the stock MCU and the MCU with Sleep and Musik's mod?

Thanks.