The 2-D is a terrific camera in many respects, but it is HEAVY compared to many expensive modern cameras in the same formats. How "portable" it is depends on your standards for portability, but it's hard to beat on bang for the buck.
I've just expanded from 5x7 to 8x10 (both 2-Ds as it happens), and the difference is pretty significant in terms of the logistics of handling the film and the scale of operations on the camera. In some arrangements with the 8x10 I can't reach the front standard from under the darkcloth, which is all right if I plan for it (it means using rear-standard focus for final adjustments, mostly) but was pretty distressing the first time it happened.
Normal lenses for both formats are reasonably available without breaking the bank. A 210/4.5 Tessar type is a good-sized but manageable lens; in the 300mm length I expect they're more likely to be f/6.3.