For my linen closet, I used oak molding for cleats and cut oak ply for shelving.
It was a weekend project as I polyurethaned the oak.
I finished the cut edge with screen molding.

Everything was easy to do and I bought everything at Lowe's.

You might also check out an unfinished furniture store; you could be surprised.

I installed those metal shelf standards & brackets

and put wooden shelves on them.

I used plywood--had a lumberyard cut it to size, and got some iron-on veneer tape (and a little squeezer thing to shave the edge-banding down to size).

It worked great.

The brackets get in the way sometimes, but they're very adjustable. Cleats, while strong, are not; they're permanent (which is sometimes what you want).

As for dimensions, well, anything will work in the right situation.

Look at the shelving you have in other places, and see what it holds well. Bookcases are often 8" deep, and thatholds more than you'd think, and is good for smallish things (cleaning supplies, craft supplies, etc.); utility shelves are often 12" deep, which is too deep in some situations, too short in others. If you want to store big storage bins, you might need more like 24".

Ihave a closet that's long and skinny like that. Where is your door? Is the closet open all the way across the 30 feet, or will you have to scooch down in front of the shelves?

I would say, do those standards and brackets. Less work, and greater flexibility.

You can buy longer or shorter brackets for different sections, if you want, without having to do anything more than install a shallower shelf. So you could have 24"-deep shelves using . And you can swap out the 24" brackets (or 18.5") and use 5" brackets in some other section where you want the shelves to be shallower.

You could even install heavy-duty ones ($) in one section and light-duty ones () in another.

I would also say, w/ a length of 30 feet to cover, that you should think of it in terms of 36" to 52" sections or something--so you can adjust the shelving to be different from one section to another, and so you don't have to wrestle some huge long boards around.

For example: Measure 2

It's 23.9 inches end to end, so let's pretend you have room to store it end-in on a 24"-deep shelf. That means two of them side-by-side (at 15.9"wide) are 36" wide; you need a 36" space between the brackets. (You want this, because you want to be able to slip the Rubbermaid bin all the way back to the wall, and not get hung up on the bottom of the bracket as it angles down.

The standards themselves are 1" wide; the brackets a tad less. Go w/ the 1", and figure drilling the holes 1/2" on the outside of each end that 36" space (holes are then 37" apart).

The shelves need to be the 36" plus 1" on each end to get to the outside of the standard & bracket combo (38"). I don't know for sure whether you need to have an extra inch or two to the ends to go BEYOND the standard; if you attach that shelf to the bracket itself, you may not. In most of those systems, there are hole in the underside of the bracket', and you can put a pair of long screw up into the shelf from the bottom.

Change the dimensions to match whatever storage things you're using.

And of course, worry about sag--the can help you figure out how much weight the plywood will hold between the brackets. (and maybe, just maybe the extra wood that sticks out beyond the bracket will held work against sag, but maybe not)

If you want a longer shelf, you may find you want a middle bracket to avoid sag, so plan its placement as best you can, based on what you'll store there.

You might consider having one section that's just for big storage bins like that, and measure a few different brands to see if there's any commonality you can count on (or, commit to a brand, and buy a bunch). And other sections could be made to hold slightly smaller bins, or to have open areas for just stuff.

I installed shelving like this and wanted SIDES, so stuff couldn't fall off the edges. I attached a vertical piece of wood to both ends the top shelf using L brackets, and then used L brackets to mount it to the wall midway down so it wouldn't wobble.

I can still adjust the shelves between them. (I did it this way instead of a bookcase because the left side couldn't go all the way to the ground, or I wouldn't be able to reach the radiator valve)

In the living room especially, I didn't want the shelves to bump up against the brackets and leave a gap behind them, so I cut a notch where the standards were. (next time, I'm going to use a hole saw to cut a semicircle there, isntead of trying to use a jigsaw to cut a 1.25" x 1.25" notch--those corners were a pain) And the shelf slides up against the wall. (if you do that notch thin, you'll need 25" deep shelves to go on 24" brackets.

I even painted my standards to match the wall, and used white brackets to match the white shelves.

If you wanted a section w/ a hanging bar, you could either install a hanging bar to the underside of the shelf, or try to find a standard-and-bracket system that has a hanging-bar type component. Or, maybe get two 18" brackets, and wire (or weld) a bar to the end of the bracket)

If you have to go scooching by (the way I do), you could probably go w/ 16" deep shelves, and fit the big bins in sideways, and smaller bins in end in.

this small-ish Rubbermaid one is 15.8" end-to-end, which makes it the same depth as the big one is if it's placed sideways.

And the clear shoebox size ones are ALSO 15.8" end-to-end, so they could fit on 16" deep shelves nicely, end in.

Once I started digging around under "Products / Storage" at Rubbermaid.com, I found that lots of their containers are just under or just over 16" in one dimension or another.

So at 16" of storage, in a 45" deep space, that leaves you 29" for your body to stand in as you scooch by.

(I'll measure my "scooching by" space this weekend if you'd like--I have enough, not too much, but enough)

You could even do double-deep shelves going crossways across the end.

And you could do deeper shelves over your head; just be sure you have room to get whatever it is, down between the shelf edge & the opposite wall. But you don't have to have room for you, too.