Well for one he wanted the right time to get attention with Kyuubi to mask as "Madara" then he needed a group powerful enough to subjugate all the Bijuu's and needed Nagato, who had the rinnegan, to do it. So he manipulated him, and at the right time, when sasuke finally disposed of Itachi, who would of interfered, Obito approached him to deceive him as well in order for him to use the rinnegan to revive madara again.
No, it was all part of madaras plan. Him taking madaras name was his idea though. He dosn't care about the world, so I doubt he would be afraid of anything in it, including itachi.