In the games, Sonic has never officially had a love-interest although it has been hinted time to time that he secretly loves Amy, while in the 1992 Shogakukan manga (where she was known as Eimi the Hedgehog, Amy Rose's earliest incarnation) and Sonic X, he loved her. … ... Lara-Le.
Lara-Le of the House of Arian
Is Dr Eggman a robot?
As a Robot
Roboticization - Whilst he was still robotic, Dr.Eggman was briefly capable of roboticizing living creatures merely by touching them. Of course, he lost all of his mechanical powers when he was deroboticized by the Bem.
The highest official description of Sonic's speed labels him as hypersonic, or somewhere around Mach 5 to Mach 10, and this actually isn't too far off. In Sonic Unleashed, passing through a checkpoint records his speed, and he can reach a maximum around 3,500... SPD.