Most suggest 6 feet between vines, so 7 feet is fine. Treated lumber uses copper, I spray copper on my trees. Use the treated lumber. The old arsenic based preservative works really well to preserve the wood, but they quit using that in 2003. The new copper stuff is better than untreated wood, but not by much, still i would use it.
Well metal can be used. It certainly will never have to be replaced.

Most folks use wood, not metal posts. There is a big price difference between 4x4 vs 6x6. The 6" round posts are cheaper, but the big box stores do not sell them.

There are tons of resources out there. But most of them are geared to commercial growers, like rows of 500' long rows. Not a lot of info for home growers.

I agree most commercial growers use wood but I have 24 foot stretches using metal. No anchor either. I have some wood too. As far as what is used I would disagree as far as the home owner. Most home owners have grape vines on fences, metal fences. Not a good idea, but so many do it that way.
Here a trellis for raspberries
{{gwi:125614}}

The wires are taut using heavyduty wire tighteners

{{gwi:125615}}

Above is when i first put it in 2 years ago. it's quite crowded now.

{{gwi:48157}}

Mine is an open area, so I'll need to set it up from scratch.

Your looks nice. I think to make it easy to prune, fruit picking and maintenance, a 5' tall trellis is the best. You do not want to climb on the ladder to prune the grapes on an arbor.

The incremental cost is much lower for a long row. But for more than 5 vines, we should be growing wine grapes. I still do not know if I want to grow like 15 grape vines.

Once established they are very productive. I had 4 and that seemed to produce a lot. I removed them, and put one back. They were my dad's vines, and he passed. I don't make wine, and they were seeded, and not good fresh.
I just put one in, but it's not doing well. I may graft it unto my dad's rootstock. I kept one of his alive. With one trellis for one plant, I didn't use anchors, but anymore, you should. I would buy like 8 foot 4x4 and sink them 3 or 4 feet.
The metal conduit works good for raspberries they are not really heavy and only need it when fruiting.
Well have fun, it will be cool! Seven sounds like plenty to me. Add Kiwi vines, or grow blackberries or raspberries.
Espalier trees on a trellis. Make a currant cordon. Lot's of other fruit you can put on a trellis.

This post was edited by Drew51 on Wed, Nov 19, 14 at 15:24