I’m currently doing something a bit similar - 3.5 year BS with 1 co-op, 5 year MS with 2 co-op’s total undergrad and grad. As long as you bring a reasonable plan to the table, they will help you with doing whatever you need to do. You will have no problem with a 3 year BS.
Northeastern hasn’t really pushed one plan more than another in my experience - that may be more on the admissions side. Sit down with your advisor and share your plan, and it should be very doable given the proper credits line up. They will likely be more than happy to help.
I know people who have done similar - some even graduated undergrad and grad at the same time by technicality. It’s very common and possible for those doing a +1, though I haven’t heard of many graduating early undergrad who didn’t go that route.
One thing to note: a lot of upper-level classes are going to be a lot scarcer in the summer - make sure the classes you have lined up for the summer are available. While there is still a good deal offered, that 3000 elective in particular subject X probably isn’t. If you line up your lower level classes to summers, you can probably still manage.
Additionally, if it doesn’t line up, graduating in December is pretty common - don’t be afraid to do a 4.5 year MS if needed, etc. It may make more sense when you get into the nitty gritty details, may not, but plans change a lot. I also mapped out my full schedule before arriving, and saved it just for fun. The skeleton held, but plenty changed and you should be ready for that, as you probably are. My 5 year plan and degree plan still held, but even my co-op schedule changed over time, as well as classes of course. As long as you have a handle on where you are currently, you’re good. Just something to keep in mind.
Given your situation, it all looks good to me! You’ll still get a full college experience with 4 years, and you’ll get two degrees in the process. Kinda my thought process with 5 year MS, as nearly all of my friends do a 5 year plan so it wouldn’t feel like staying longer. People will understand 4 very easily when it comes to your friends, so that should be good as well.