It has some limitations
I don't have the 4x5 but I do have the 6x9 Tech III. The camera is astonishingly well made and a joy to use from a mechanical perspective. However, be prepared for some limitations with this older model. Most noticeably, when using wide-angle lenses. I use a 65mm a lot and I have to use some front rise to avoid the focusing rails appearing in the image. Additionally, I have to use front rise to be able to use ND grad filters otherwise they'll only slide a short way down the lens. You'll experience similar problems with a 90mm lens on the 4x5. Additionally, the Tech IIIs don't have front tilt other than by dropping the bed which can be a limitation although you can get similar results with the fiddly rear tilt.
The rollfilm backs are plentiful on eBay and if you wait for a bargain you'll definitely find one.
My Tech III 6x9 weighs 4.5lbs + lens so about 8-9lb in total. The 4x5s are about 6.5lbs + lens and back so about 10-11lb which puts it over the limit of your tripod. On the other hand, because I hike a lot, I use a very lightweight Gitzo 1228 with Arca Swiss Monoball and the 6x9 is rock steady unless the wind is really gusting.
Have fun.
Barry