A Cuban IT Group implementing Asterisk

Hello everybody out there! (sorry for my english)
We are trying to implement Asterisk as a VoIP PBX in our job, we already have a Mitel SX-2000 and we want to keep both services during a certain amount of time, to do this, we are plannig to buy some things:

We need oppinions from someone with experience to know if these things are enough to implement Asterisk.