you can do this and there is nothing wrong with it. Book the first 4 days and then call back and book the next 3..link the ressies. Just know there is a chance you will have to move, but it isnt likely.
when you used moms credits just do it in a way that it benefits you most..snacks/desserts or drinks you can use after your ddp has ended
You can use your credits up until midnight your check out day(day 4 in your case) so you could use moms extra credits to feed people 2-3 times on a couple days. make full use of your check in day and check out day(of the first part of your stay) moms credits wont last long that way and you wont be cheating the system