Not personal experience but from what I hear pressure-treated wood would last 20ish years, and creosote-treated timbers you might not want to use near your fruits & veggies. I think there is some controversy here but at least make sure to do research before installing anything chemically-treated near food. It is done and may be your easiest/cheapest option but just be aware.

I used Allan Block concrete pavers to build the terrace in my back yard -- it's heavy work and the pavers are not cheap, but it does look very good. If you can get your hands on native stones it might be cheaper and maybe you can build a hodgepodge wall.

To build a retaining wall properly, you have to dig up a lot of soil and lay down gravel and backfill with gravel. For all that work I'd recommend getting a bobcat or something that can dig out a lot of dirt quickly. Shoveling takes a long time even for a small wall (mine was only like 10' long) and if you have any trees nearby, it's orders of magnitude harder. Depending on your climate you may not have to worry about frost heaves and then maybe you don't need to dig as deep. It also depends on your soil.

By the way, in my town you need a permit if your wall drops more than 4 feet. If your separate walls are closer together than a certain distance (maybe 8 feet?) then the town considers them to be one wall. So even if you don't consult your town it may be worth consulting a landscaper or engineer.

Due to the amount of labor in properly building a permanent wall that size and since you only need 1 foot drops, maybe you can just form a row of native rocks and backfill with soil without digging a trench? Since you have 6 of these 1' drops though, I'd check with a pro to see if this is a good option.

Re. whether the walls are do-able, you need better advice than I can give you.

I think your first task -- before designing the terraces and aisles -- should be to figure out what you want to plant and how much space you'll need for it, including the space taken up by the walls and aisles. Plot it out on graph paper. I suspect most of the 40' x 40' -- maybe all of it -- will be needed for the trees, grapes, and berries, and you'll need a second garden somewhere else. Of course some of that will depend on what kinds of fruit you're planting, and whether the different varieties are self-pollinating or not.

I have (young) dwarf and semi-dwarf fruit trees planted in rows; the dwarfs are planted 10' apart, the semis 15' apart. The rows are 20' apart. I thought for a while that I should have put the rows closer together, but at this point I've begun pruning the oldest trees to be short and wide (I'm barely 5' tall, and I don't do well on ladders), and I'm afraid I should have put the individual trees farther apart....

If you do figure out a way to build your terraces, the grapes and berries will lend themselves well to that layout. I'm not sure about the trees, though. Maybe you should do a sideways elevation plan -- a cross-section showing the different levels and what's planted there; draw the height and shape of the trees and berry bushes. How will the 6' wide terraces work with 10' wide fruit trees? Will the terracing cause any difficulty when you're harvesting from the trees, or pruning the trees?

My five oldest apples, planted by the Previous Owners, are on a slope (the area under the downhill halves of each tree is almost as steep as your slope), and I definitely wouldn't want to deal with terracing when pruning or harvesting. I'd back up to get a better view of a branch that might need to be pruned ... and fall backwards over the uphill terrace wall. I'd look up at the top of the tree, get dizzy, lose my balance ... and fall off onto the next lower terrace.

You won't need to till under the trees, and hopefully runoff won't be a problem there. So you might want to forgo altogether the idea of terracing under the trees.

This is pretty basic, but just as a reminder: when you're planning what to plant where, be sure to take into consideration the sun exposure, the height of the trees, bushes, and vines, and the shadow cast by the barn.

I also have a gently sloped yard in need of some terracing. When I look at pictures of the ruins of Macchu Picchu I don't feel so bad about what I have to contend with! Anyway, what helped me with spacing and placement in a veggie garden (which I have yet to plant but is now thoroughly "planned") is this cool garden software from Shumway's. I think it was free the first month too. I think other online garden places offer the same kind of software too. You can place the walls of the terrace using thick lines and then the plants you place are automatically "spaced" at the distances they are supposed to planted at (I think if you pop in companion plants they can be planted closer). What I have done in the past is to place cut logs (i used pine), say, 10" diameter firewood type pieces and put them all up on their side all in a row, to create short terraces. Then, because they will only last for a few years, you can collect the rocks you want in the future and replace the wood as you go. You could do a few of the terraces with bluestone slabs and a few with rounded small boulders. You might be able to get some cheaply from local farms, they tend to make piles of rocks they find in fields while tilling. Also, they may be able to arrange for you to have a dump trailer of manure brought in to improve the soil. I would add about 10 yards of manure and/or compost to bring it all up about 2" (it will give more than 2" if you leave out the compost along your pathed areas)