Back to the OP's question about the cost of metal field cameras in 4x5, there aren't nearly as many metal as there are wood, especially in the under $1000 territory. You might be able to find an older Toyo 45A that would be all-metal, and a very versatile camera, in that range. You might also get lucky and find a used Canham DLX under $1K, but that would require luck. And it's a different design than most, so I wouldn't recommend it as a first 4x5 (I do highly recommend it as a view camera, just not a first one). There are gobs of monorail cameras out there that would fit your bill, though. Frankly, I'd look for a Sinar F or F2. You'll have all the movements you need and then some, in a very reliable, flexible system camera. There are TONS of spare parts and accessories out there for it, and if you want to grow into 8x10 or 5x7 later, it is easy enough to upgrade with a new rear standard and bellows without having to buy a whole new camera.
If you are looking at the transition from portraiture on 120 roll film (in, I presume, a reflex or rangefinder camera) to portraiture on either 4x5 or 8x10, then the relative merits of the two formats have been pretty well described: cost, bulk and depth of field.
However, there is a big difference between a situation where you see the subject through the camera right up to the moment of exposure, and one where, having composed and focused and directed the subject from behind the camera, you actually make the exposure after a brief interlude of mechanical manipulation, while looking at the subject from beside the camera. Not only do you have to visualize what the camera is actually seeing, but you also have to deal with the subject's tendency to shift attention to you rather than to the camera during this interlude. Or learn to make portraits with the subject looking off to one side :)
A good place from which to explore the transition might be an inexpensive monorail 4x5 (Calumet CC400 or comparable) with a few holders and a roll film back. A "normal" lens for 4x5 makes a good "longish" focal length for 6x7 or 6x9 portraits, and you could probably use your current tripod, enlarger, etc.
When you find that you really, really want larger negatives, then moving up to 8x10 will be (relatively) painless and inexpensive---unless your interest is in silver-gelatin prints larger than 8x10!
I hate to use crappy digital terms (honestly, I hate digital), but in raw scanning terms, 4x5@4kdpi is over 300 megapixels and 8x10 is in the gigapixel zone. These are way beyond anything purchasable today with reasonable amounts of money. "Old" technology once again wins here. Cost-wise, medium format digital backs approaching 50-60MP are like 20 grand. Do the math (and then remind yourself it's not all about math because analog is a non-linear medium).
The OP did initially ask about photographers and while there are numerous examples of portrait and fashion photgoraphers using large formats, thought I would highlight one of my favourites, Evelyn Hofer who died four years ago and really should get more attention. Nearly all her work was shot on 5x4 and were mostly portraits. Black and white in the main, but also some colour which was printed as dye transters for exhibition. I believe she was printing her own 20x24 b&w prints. Steidl published an excellent monograph of her collected work though there were several city travel books published from the early 60s onwards which were mostly portraits. (London, Dublin, New York, Washington plus) These can be bought quite reasonably on abebooks.com.
Here are some links;