Post a picture of your pot/gourd! It sounds neat!
One of the first arrangements our floral design students work on is a triangular one, which I think would look pretty cool in the pot you’ve described. The nice thing about a triangular arrangement is you can establish the triangle with the larger, bolder material, then start filling in. It’s pretty easy.
Height? About one-and-a-half times the height of your container is good.
If you want to make it truly triangular, you might want to get a piece of Oasis foam (get it at any craft store) and put it in the opening of the pot so a couple of inches stick up above the rim. Wedge it in there as tight as it will go. That give you the ability to place some material so it sweeps or trails downward.
Pick about five different kinds of material. (Odd numbers of things are more interesting visually than even.) More than five, and there won’t be enough of any one thing for visual impact. Pick a variety of shapes and textures. You might want to pick something big to create a focal point for the arrangement. I like lotus seed pods.
If you don’t want to get something fluffy and fine-textured to fill in (like dried baby’s breath), get some Spanish moss (craft store again) and use it to fill in any spots where the Oasis shows.
Will your arrangement be sitting where it can be viewed from every side, or will it be against a wall? That will be a factor in the way you arrange.
Real cattails will shatter at some point and distribute fluff all over the place. My mom used to spray them with hairspray to prevent (or forestall) that. Dried seedheads from grasses (like pampas grass and the like) will do the same thing eventually.
(Do you have cats, by the way? I’ve never met a cat that did not LOVE to eat the stuff in a dried arrangement!)
I think feathers (like long pheasant feathers) look beautiful in fall arrangements. So do branches from twisty plants like contorted willows or filberts.
If you really want it to be permanent (as opposed to just lasting through, say, November), check out the stuff you can get in the floral department of a big craft store. They have some damn fine fake cattails, for example.
I’ll try to find some links to pictures for you. Our advanced design students do AMAZING things incorporating materials like beads, moss-covered spheres, etc. Just depends on how natural you want to go.
The great thing about a dried arrangement is that you can fiddle around with it kind of endlessly. (You might need to buy a new piece of Oasis, though, if it gets too poked full of holes.)
Oh, yeah. Post a pic of the arrangement when you’re done, too!