New Network and Server project

Just took over as IT Admin at a SMB. First project they want done is replacement of their existing network and domain (replace/re-purpose servers and PCs as needed).  They 2 primary locations in two cities with about 10 satellite locations with 1 to 4 PCs each that do not need to connect to the network (they only perform cloud based SAAS interactions). The 2 primary locations contain 3 separate businesses owned by the same parent company. The primary business has active users approx. 20 hrs/day and can survive short periods of downtime without a big issue. The secondary has active users 24/7 365 and cannot afford downtime loner than 5 minutes. They do need to share information and resources across the network as well as applications and data (SQL). The Primary location has a 10m/1m wireless internet with 1.5 T1 backup with onsite natural gas generator for power outages. There are approx 40 PCs connected with about 30 users at a time for 10 hrs/day and 3 for the rest of the day. The seconday location has 20m/3m broadband with 1.5 T1 backup with onsite diesel generator for power outages. Both have server racks installed on site but only one server in each rack, over 10 years old. They also have 2 tower servers with 2008 r2 that are onsite but not being utilized. They are custom built and have AMD FX 8150 processor and 16 GB RAM. My thoughts were to get 2 PowerEdge R520 servers with dual xeon 2420 2.2Ghz and 64GB RAM, Server 2012 Standard with 2 license, 6 600 GB 15k SAS drives in OBR (one for primary location and one for secondary). I would then re-purpose the 2 existing 2008 servers as alternate DC DNS boxes (1 at primary location, 1 at secondary). The new servers would each have 3 virtual servers (1 DC DNS DHCP, 1 for File/Print, 1 for SQL). I would have a NAS at each location for local backups and a cloud backup service backing that up for offsite coverage. Adding 1 SONICWALL 01-SSC-8753 TZ 210 at each location and 1 SG300-52P Cisco L3 Switch at each location. Looking for thoughts and suggestions?