1. Electrons from the H on the HCl get dumped on to the chlorine. That hydrogen gets grabbed by the alcohol. This forms a leaving group (water), and a tertiary carbocation (Sn1). The Nucleophilic Chlorine attacks the carbocation (electrophilic) from either orientation of the molecule not just the backside (Sn1). Leaving you with a final product that is a racemic mixture.
2. Simple distillation is only used when products in a mixture have very high boiling point differences.
2-chloro-2-methylpropane = 51 C
2-methylproan-2-ol = 83 C
Simple distillation to separate is feasible.
3. answered above.