I'm currently a college student about to finish my IOP program so I think I have good insight into this. I've done a combo for IOP while taking time off school, then being part-time school and IOP at the same time. I went three times a week, but my program has a 5 time a week option, and a php program option that I have not done.
1. The quality can greatly depend on the program, don't be afraid to shop around if necessary or feel bad dropping if you are not compatible with it
2. Yes there are absolutely suicidal people there!! I would say it is quite common actually
3. At least at mine, which I think is the common set up, there is a mix of what I would call therapy classes, therapy/process groups, and individual meetings weekly with a therapist and psychiatrist. By therapy classes I mean the will be a trained clinician that teaches about what DBT is for example with handouts and instructional videos and everything. A process group is more talky and less structured. You can choose what to go to at mine.
4. I absolutely think you get more out of it by being more active and I would argue community is a large part of the healing process, but I also think it was helpful to me when I was less interactive. I still get to hear other people talking about their stories. Almost everyone starts off shy and quiet and normally warm up later. People are generally more understanding than usual, you won't be judged for sitting in a corner and not talk to anyone for weeks don't worry.
Do know that the relationships/interactions you have with others are indeed apart of the therapy so try if you can, even though I know it's really hard
Some general bonus thought (yay!)
I think at least for me it was great for stabilization to allow me to transition to more typical therapy sessions. I do think I have reached a point where i'm starting to get less out of the program, they are generally not meant to be long term things. I think it's normally for around 8-9 weeks? Some people are absolutely there for MUCH longer though this isn't a strict limit.
It can be very emotionally tiring. A lot of people talk about returning tired at the end of the day bc its hard work. Especially as a student who still has school work to do while processing genuinely difficult emotions. I definitely needed to bump down to a smaller course load, but if that depends on how you feel
I think I grew as a person much faster because of this program. You are basically dedicating hours of the week for personal development. It's like a visible noticeable change, it's really nice.
I'm not sure where your at in life/recovery, but at least being in treatment program I feel helped my school and professors take my disability and mental illness struggles more seriously. Using my IOP psychiatrist I was able to get housing accomodations pretty easily. It also helped me take myself and my struggles more seriously.
Sorry for this hella long essay and if it was redundant at all. I hope it was useful at least?