Hi Camille,
You have an excellent eye for detail and you did a really good job at self assessing your work. I work with walnut ink almost exclusively for practice and it looks fine to me. Once you try a few inks you will develop a personal preference.
In terms of the nib scratching and ripping the paper, be sure you have properly prepared the nib. This can help smooth it out. Be sure it is inserted into the nib holder properly and watch your angle. If all of those things don't help, you could just have a bad nib or it may smooth out a bit with further use. You'll only know with a little more use. If it continues to be scratchy or gets worse, bad nib. If it smooths out a bit, it just needs a bit of warming up. I find Nikko G's do need a bit of warm up before it is smooth.
I would suggest practicing daily if you can and do a warm up sheet of those first strokes. You will find in a week or so that your consistency greatly improves.
A few notes for your last piece:
Your t's are a bit too tall. They are shorter than an l or b. Same for your d's. Look at the worksheet and note their height in comparison to the h's and l's.
Watch the shape of your a's. You want a nice oval and you don't want the second stroke to bump into the oval.
The spacing within the words is a little squished. The letters need a little more room to breathe.
Overall, you are doing very well. You have a good eye and good letter forms. With more practice, you will be doing great!