If you can afford fiber that is the way to go. It's marginally more expensive than copper, but much more reliable. Plus, since it's glass, takes the whole grounding/shielding thing out of the equation. At least for your trunk lines running to each remote location.
Assuming fiber to be out of question, let's go back to your direct burial point. Even if a cable is direct burial rated, never ever bury it directly. Always put it conduit of decent size. You will regret a direct burial install if the line ever needs to be upgraded or replaced, or if you want to add more lines to the same conduit. (Never say never). Most direct burial cabling includes an RF drain that effectively serves as a ground wire like you describe, however that's contingent upon using shielded connectors/keystone jacks from end to end, and grounding the switches to your true electrical ground/neutral. Direct burial is some very thick and non-flexible wire so don't expect to crimp an RJ45 on it or anything like that. It will most definitely need to be a punch down block of some sort, such as a keystone jack or patch panel. Also, be sure that wherever you are purchasing the cable that it is pure copper. Avoid CCA like the plague (copper clad(coated) aluminum, especially so with long runs. While the standard dictates that 100m is the max, I've encountered contractors running lengths doubling that and still have excellent communication over those links. To say it won't work beyond 100m is false; it's just no one can guarantee it and you're on your own if you have issues.
As far as the cameras are concerned, I would recommend a Hikvision or LTS based system. LTS is nothing more than a rebrand of Hikvision equipment (which is made of very good hardware) but their support and warranty is much Better than Hikvision themselves. Nelly's Security is another reseller that sells unbranded Hikvision devices while still offering a similar level of technical support and assistance. I've personally never used LTS but I read great things about them. Nelly's I've dealt with on multiple occasions and they were always very courteous and helpful in assisting me with whatever issue I was calling about.
Since each remote location has power, you can either get a PoE switch (most 5 port switches only have 1 PoE port so this may not work) or power the cameras through a separate 12V power supply.
Camera: get any of the EXIR turrets. I have experimented with several types of cameras and the IR on those is great for the price point. Yes, there are much higher end cameras that will do a better job but you'll be paying for that of course. I'm not a fan of bullets (spiders love them for some reason, haven't figured it out), and the domes are good but the IR is just not as good as the turrets.
Recorder: DS-7608NI-E2/8P
LTS equivalent:
http://www.ltsecurityinc.com/nvr/embedded-nvr/platinum-network-video-recorder-nvr-ltn8708-p8.html
Nelly's equivalent:
http://www.nellyssecurity.com/hikvi...nnel-poe-plug-n-play-hi-def-nvr-recorder.html
Sent from my iPhone using Tapatalk