@Firsttimenovelist everything splishsplash said 😁
I'll try to cover some of the other points in your post?
So I don't actually use a professional editor but I'd just say do your research before you choose one. There are editors and there are editors. You want someone who is going to add something to your writing and not just get tied up in grammar and kill your voice in the process. Grammar / typos can be easily dealt with in Pro Writing Aid, and then try to have a first reader to catch typos. Mine is my gran and a superfan who do it because they love my books and want to read them early. You can try joining groups with other authors like Alessandra Torres Inkers, or Lee Savino's Author Mastermind and ask for recs. OR usually authors will credit their editors in the copyright pages, so check in there if you feel the author has a similar style to you.
Same goes for cover design. Use the look inside feature on Amazon on covers you love, and see who their designers are. It will vary depending on genre but if you let me know, I can point you in the direction of some good ones. They all mostly use groups on Facebook. Premades will be a lot cheaper than customs, but if you're on a very tight budget please PM me and I'd be happy to help come up with something for you.
MS word is totally fine! If you decide to get serious about it then you might want to look into Scrivener. This is a program basically built for manuscript writing and you can have chapter notes, rearrange things easily, keep an outline, add photos from pinterest and character notes etc. Word is completely fine but this just makes everything easier, and it exports easily into Vellum.
Re clunky dialogue I'm sorry, I can't even remember 🙈 I have conversations in my head ALL the time and sometimes just type them out in my phone. I earwig into conversations a lot and make little notes. When I'm watching a film or TV, if people say something I like / find interesting I make little notes about what I liked, or how they did it. Basically become a creeper with a phone full of good words and sayings 😂 and just practice writing out conversations. I did a lot of this (and still do). Conversations that will never be published but are interesting. A girl on her first day in a new high school with an asshole teacher. A police officer dealing with a drug dealer. You get the idea. Also read a lot.
For the actual technicalities I recommend this book! The Dialogue Thesaurus by Dahlia Evans (it's on kindle). I'm still practicing getting this in on the first draft, as it doesn't come as second nature. Don't be afraid of using "I say, I said, he said, she says." What I mean is don't always try to edit this out for "he moaned. She whined. He mentioned. I exclaimed."
"Say" and "said" just vanishes for a reader. They literally gloss over it. But always exchanging that for a "better" word can get really distracting. If you need to use:
"I won't do it," she declares.
Try:
She sticks out her chin and squares her shoulders. "I won't do it."
This makes it clear who is saying it, and that she's declaring it, and it lets the reader actually see it in their mind.
Hope that helps 