VPN site to site and other services

  1. Which Mikrotik hardware and software (RouterOS level) do I need?

the rb1100ahx2 is the best hardware for central office, en the remote office you can use a rb450G.

  1. The hardware in the central site is capable to support the seven tunnels at the same time?.

yes,

  1. VoIP to be implemented in the future, Mikrotik has any hardware that could run Asterisk?.

yes, read the metarouter with asterisk from http://forum.mikrotik.com/t/metarouter-images/28791/1