[GpsFrontier]

GardenState

It sounds like nft is the preferred outdoor technique using some sort of pipe or gutter.

Preferred? That depends on who you talk to, what your growing, as well as many other factors. There are 6 types of hydroponic systems, and though many commercial operations use NFT systems. Their typically only used for small fast growing plants like lettuce, and inside a climate controlled greenhouse.

My concerns are the res and the very difficult task of burying anything without a backhoe.

One way or another you'll need to be able to keep the nutrient temps under control. Using a NFT system will make that much more difficult, not just water temps but root zone temp (that's why their typically used in climate controlled greenhouses).

And power failure leading to the quick death of plants.

That is another drawback of using a NFT system. It relies a consent flow of water to keep the plants alive. Short interruptions (10-15 min) probably wont be much of a problem, but because the roots are essentially hanging air, they will dry out very quickly. where roots that are surrounded by moist growing media will have access to that moisture until the growing media becomes dry.

How do you size the res? How many gallons per plant.

These numbers are minimum recommendations. I generally try to double the minimum recommendations in my systems to avoid fluctuations in nutrient concentrations and pH (especially as the plants reach full size). General recommendations are 2.5 gallons (per plant) for large plants like tomato's, 1 to 1.5 gallons (per plant) for medium sized plants, and .5 (1/2) gallons (per plant) for small plants like lettuce. That goes for any hydroponic system, however sometimes in some flood and drain systems, they may need more water to keep the pump from running dry during the flooding cycle as the plants drink up the water daily.

I also have a problem with very high Ph (8) water. So the res can not easily be topped off without PH correction. So if away for a few days there has to be enough water. Or is there some sort of cheap way to auto correct this if I use a float valve?

PH 8 isn't far from neutral (witch is pH 7). What water are you planing to use? Using just plain tap, softened, or well water may lead to other issues regardless of pH. This is one of the problems of using a reservoir that's too small for the situation. As you mentioned and fintuckyfarms suggested, using a float valve to keep a consent water level will definitely help. But still may be a problem if the reservoir size was/is to small to begin with. Including if the plants drink up too much water, and/or if your not replacing it with pH adjusted water. If the reservoir is to small, the nutrients in it will be depleted too quickly, even if the pH is correct and water level continually filled.

Also can you use one res for multiple plant types? Is there a happy medium for the food. Something every plant will like.

Yes you can grow more than one crop in the same system. A happy medium? It depends on the plants you plan to grow, but there will always be a compromise. That's why the type of plants grown, what stages their in etc. will determine how happy that medium is. Something every plant will like? No, there's no magic formula that's perfect for all plants. There basically broken down into two groups, for vegetative growth, and for fruiting growth. But grouping your plants/crops in one system with similar needs will give much better results than not doing so.