Do you find the 303 scratchy? I like the 404 better.
I can see this version really well. Your Spencerian is beautifully consistent! Do you find it confusing to work on both simultaneously?
Spacing and sizing can often be a matter of preference. Your Spencerian minuscules are just slightly on the tall side. They are still very pleasing but traditionally, I think Spencerian is a bit shorter so one would use different guidelines than what they would use for Copperplate. Other than that - Wow!
Copperplate is written at a slower pace than Spencerian. There are a few words where the letters feel a bit rushed. Watch your spacing between s and h like in Bush, Clash, and Rush. There needs to be a bit more breathing room.
The only things I would suggest you could work on would be squaring tops and bottoms and your s. It looks like you are making your Copperplate s the same way you make the Spencerian s except with shade. Traditional copperplate makes the s very differently. At the least, I would not make the shade start at the top.
I hope that is helpful. You clearly have worked on your letters for some time as they are very beautiful and well made.