You should consider one of those program that help cleaning images from text etc. As for the cover if you want to clean it you should put the title at the bottom not in the middle
Are you going to work on other works from this author? Apart from the ones in this series (wich btw the first and third part are my favorites, the second is so-so), like the fate doujins or even some of the pixiv shorts?
Heyya, since you asked I have a couple things to say about the translation/editing. I would have chosen a lighter font maybe, it looks much nicer if you aren't hugging the edges of every bubble. A few bubbles don't have the text centered vertically which looks off. You missed capitalizing words and "I" several times, plus a few missing commas a free grammar checker finds those pretty easily btw, I'm guilty myself lmao. I think you should have done the moan bubbles, but eh. As for the translation itself, I didn't look for accuracy, but the wording I assume is following the Japanese sentence structure pretty closely. This gives some sentences a weird feeling, so if you plan on continuing translating, just keep an eye out for sentences that feel weird or stiff, and don't be afraid to restructure the sentences in different ways. This is actually pretty difficult to learn tbh, took me several translations before I got comfortable with it.
Your translation is actually very good for a first effort! If you want extra help, the EHcove group on the E-hentai forums can be a great help giving advice and checking over your work.