You had said in your OP that you would like IP and PoE, but I don't see where you have specified a VMS or if you have existing PoE hardware. I am going to assume you have nothing, so you don't forget anything. Obviously, if you have some of the components, simply ignore my suggestions.
// HEAD END //
VMS Software - We usually use DW Spectrum due to the low cost and it's very easy to use
VMS Server/Worsktation - We usually use a Lenovo barebone PC with an Intel i5 CPU, add an 8GB RAM, nVIDIA graphics card, SSD for the OS, and WD Caviar Purple or Seagate Surveillance hard drive(s) for video storage (whichever is a better deal ATM), and Windows 7 Pro x64.
PoE Switch - For this small of an install, I would lean towards a Ubiquiti ToughSwitch Pro 8 Port switch, but if you need more than 8 ports total for other devices, you may choose to go larger. UBNT also makes a 24 and 48 port PoE switch that we use for larger installs. They are very cost effective and have been rock solid reliable for us.
Battery Backup - We always use a UPS at the head end. We commonly use a CyberPower 1000va unit, but if you desire more runtime, this is the baseline. Feel free to opt for a larger unit if desired. We expect no more than 30 mins of uptime from 1000va.
Peripherals - You will also need displays, keyboard and mouse, etc. These are 100% personal choices, depending on your budget and needs.
Wire - Obviously you will need CAT5/6 wire and connectors.
// CAMERAS //
I am going to assume aesthetics will be considered as well as performance, so I will try to balance the two. I know that some others here prefer the bullet or turret form factors for performance reasons. However, I really don't like the look of either and feel that bullets are more easily tampered with. We don't have issues with IR reflection in the domes we use, so that isn't going to keep me from using them. These are my personal reasons and may not apply for you. Take this with a grain of salt.
As to the weather in Montana, I am not from that area, so I really don't know specifics. I can only go by what we have installed here in Ohio, which isn't exactly the tropics either. If you need units that are rated below -20C, let me know because I will have to rethink my choices. I know that we have cameras installed here and it has dipped well below -20C and they haven't had any issues, but that doesn't mean it is the proper choice either.
CAM-1 - Dahua IPC-HDBW5302 3MP Dome Camera 3~9mm Motorized Zoom Lens 65' IR
CAM-2 - Dahua IPC-HDBW4300E 3MP Dome Camera 2.8mm Fixed Lens 100' IR
CAM-3 - Dahua IPC-HFW5300E-VF 3MP Bullet Camera 2.8~12mm Varifocal Lens 100' IR
CAM-4 - Dahua IPC-HDBW4300E 3MP Dome Camera 2.8mm Fixed Lens 100' IR
CAM-5 - Dahua IPC-HDBW4300E 3MP Dome Camera 2.8mm Fixed Lens 100' IR
I don't know where these cameras will be mounted. You may need a backbox or wall bracket for the domes. I will list the appropriate part numbers below.
CAM-1 - Dahua Wall Bracket (PFB300S), Pendant Cap (PFA100), Back Box (PFA120)
CAM-2,4,5 - Dahua Wall Bracket (PFB200W), Back Box (PFA131) or (PFA123)
CAM-3 - Dahua Back Box (PFA121)
// CLOSING //
That's about all I have to offer, unless you have more questions or concerns. Feel free to ask away.