Looks pretty good.
It looks like you did a good job under exposing the ambient, but a little more fill flash would help in some of the images +1/3 to 1/2 stop (+2/3- +1 works well for me in camera).
I would say don't be so weary of the flash. In some images, they still have a slight yellow/green tone to them. Adding a bit more fill flash will help alleviate the color cast from the grass and light coming through the trees, unless they are right on the grass and the flash angle is too steep, you can then start bouncing green back into their faces. This is also where a smaller softbox helps as it is a larger light source and wraps around them more.
The larger light source and a little bit more light will add color back into their eyes. Less so when you are shooting multiple people, even more so when you are dealing with one/two people or closer up head shots.
Getting the flash off camera helps as well, though this is not really an issue here.
All in all for your first time with flash these did turn out good, i would just work in PP with the slight color cast. Great expressions and i love the composition of the 2nd to last image.
I like the B&W just the way it is.