Clearing overgrowth

I have purchased several acres in the Piedmont of NC and am trying to figure out how to convert the land to a food forest. About 3 acres was pasture 10-12 years ago but is now overgrown mostly with blackberries and other nuisance plants. It does have a few edibles like persimmon and pecan. I plan to leave those in place but am trying to figure the best way to clear the other stuff. My plan is to get goats (I plan to have them anyway) and let them do most of the work. My question is how do I keep the stuff from coming back? Can I seed heavy with vetch, clover, alfalfa...? Ideas? Most everything is goat friendly but I know poison ivy and blackberries can be really hard to kill at the root. Thanks in advance.

I think goats are a great idea for taming the overgrown undergrowth. And seeding with clover, vetch, and alfalfa is a good idea whether or not they smother the re-growth of blackberries. I don't know that they'll wipe 'em out entirely, but they should help to limit. If the blackberries do grow back, just bring the goats back. Worst case scenario, you have a free source of goat food that requires no effort to grow.

I also meant to ask... does anyone know if dead (winter killed) blackberry canes are edible/healthy for goats?

This doesn't directly address your question about winter-killed canes, but this article (and many others I encountered) show that blackberry control is a very popular use of goats. If dead/winter killed canes were a problem, I think it would have come up.

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=2493

the goats ( or at least my goats ) will not eat the dead canes, they will devour blackberry thimble berry and wild rose leaves with pleasure,including the softer tips of the canes , leaving canes that are now easier to see and grub out they will also happily strip the leaves from poison ivy making the vines and roots easier to see and remove
if they are so hungry as to eat the dead canes that would be a problem . And you want then clearing but also getting nutrition
portable cattle or hog panels are an easy way to work them as if allowed to have a full pasture they take a bite here then a bite there . Pen them with ample water in small padoks and move it as they accomplish the clearing ( what ever is just outside the fence is what they will decide tastes best )
Miss my goats .

I am easily in the top 1% when it comes to clearing berry bushes. I cleared about 25000 sq ft this summer. This was done with a hedge cutter. If used along with livestock, much more could be done in the same amount of time. I could see cutting pathways to the areas in need of clearing. The goats will clear whatever is palatable, then we cut some more. Small trees could be dropped to provide variety.

Give useful trees some wire protection.

Once an area has been cut once, the goats will control regrowth, since it is more tender.

Here's a thread about cleaning trails and other areas.

https://permies.com/t/38429/projects/Dale-series-farm-improvement-projects