Hi! I'm a recently graduated BSN student who works in an OR as a nursing assistant and will transition into the RN role at that OR once I pass my boards. The comments here have covered a lot but I just want to add my two cents as I had over 700 hours of experience in the OR prior to graduating.
Regarding whether or not to do med-surg first, there's never any harm in specializing straight out of school. There's no shortage of nurses at the bedside so if you for some reason really hate it, you can just go back to the floor as soon as you want.
There are also a lot of pros/cons with larger vs. smaller ORs - I've been at four facilities so far, two with 20+ OR suites and two with ~10 OR suites. The larger ones split day shift into service teams, which can be really good if you already know what service you like(ortho, general, plastics) but can come with the downside of not learning a variety of services and being versatile. It also means you'll normally be working with the same people all the time, and I've seen that be pretty detrimental for me as a student. Smaller ORs have the benefit of fairly tight camaraderie amongst the staff, it's easier to integrate into the environment, and you can learn all the services available. I've also found that in the smaller ORs it's easier to make yourself heard as an employee, both of the larger ORs I was at didn't address full-time staffs' concerns much, if at all.
If you have the option to, teaching hospitals are in my opinion great to be at. Teaching hospitals tend to have really active nurse educators who advocate and make sure you're on track to fulfilling your orientation/residency as well. If they take nursing students/med students/residents for shadowing or rotations, it's an indicator that there's a chunk of them who enjoy teaching - and if you pick up a similar role with precepting it keeps knowledge and rationale fresh.
I would not recommend "main" campuses of hospitals overall - they're too big, staff concerns can get overlooked very easily, nurses get thrown under the bus, etc. My best OR experiences were at smaller "satellite" hospitals under the same name, and I learned more.
Glad to see more people wanting to get into the OR!