For starters, once school has been in session a couple weeks, I'd see about getting him more appropriate homework. Homework is supposed to reinforce new material you are working on in class. Yes, the beginning of school is always lots of repetition but if a month from now, he's still getting work that he can do in his sleep, seek accomodations for more challenging and engaging work. Better him spend 15 minutes on work that makes him think than 15 minutes dawdling or repetitive material he could finish in 2.
Some ideas about the homework...
If it frustrates you, don't watch him do it. Set him up at the table when you make dinner or are otherwise engaged. If it takes him the whole time, well, it's not taking any time from what you need to be doing. Don't fall into the trap of sitting next to him and watching him work.
Be mindful of when you time homework. Doing it right afterschool doesn't work for all kids. Many do better after a snack, some running around time and/or a bath.
Perfectionism is a tricky beast. My eldest has it in spades. Challenging work can be helpful. If your DS's mind is concentrating on getting the problems right, he may not worry so much about whether the letters are perfect.
Break-up the homework time into 5 or 10 minute segments throughout the day. It may seem more disruptive but it can lesson the actual amount of time your child is sitting at the table doing homework.
Find out what the reccomended homework times are per grade for your district. Ask the teacher how much time she expects kids to be doing homework each night. If your DS is spending more time than is suggested or required find a compromise with the teacher. Like I said, my eldest is a perfectionist and in elementary, tended to make little assignments into HUGE ones (like writing 3 pages on a topic instead of the half-page required.) Some ideas I got from her teachers was to have her only do every other math problem (they allowed this if I signed her paper because she was a fast learner and didn't need the amount of repetition most kids needed.) One teacher had me give her time limits on certain projects. Instead of her spending 2 hours on a paper that should have taken 15, I'd give her 30 minutes to complete. It was frustrating to her in the beginning but she did learn to budget her homework time better. This is a lesson that has served her well even now in high school. Just send a note to the teacher that time spent on homework has been an issue and you are trying some things at home to remedy it. This means he may come in with incomplete work for a bit.
I think more appropriate work is the priority though I wouldn't approach it with the teacher until the kids have been in school a few weeks.