SilviaK

Once you're all checked in, the process itself is quite fast. Depending on how busy your service center is, the wait ahead of the appointment itself can be long. I had a weekday afternoon appointment right after the holidays in NYC, but I went first thing in the morning to avoid having to leave work. At least at the office I went to, they still let me in despite my appointment being much later, and they didn't care at all when your appointment was once you were inside...it was sort of a free for all. But the whole thing took about an hour and a half for me, despite the actual biometrics only taking about 10 minutes. No interview...just fingerprints, photo, and confirmation of biographical information that you provide them with. I did a really thorough write-up of my experience in the below post. Might not totally apply to Indianapolis, but worth sharing just in case!
 

Totally depends on the location. Mine were taken in Duluth, MN.  

I got there 30 minutes early assuming that it was going to be a long time to get in and then a wait, but I walked through security in less than 2 minutes (one of the guards even took me to the elevator and directed me from there because it was a convoluted building) and the lady in the office was happy to see me before my appointment.   The longest part was waiting while she reset the computer system - I was in and out in less than 10 minutes.

I did my biometrics in Philly too and was outside in about 5-10 minutes. I was shocked, since you're right that Philly is one of the busiest local offices in the country!
If they would process the actual I-485 as quick as that my biometrics appointment was I would be so happy lol.
Off to another year of waiting! Well, at least I have my EAD and AP 

The actual process takes minutes. The total wait, however, could take anywhere from minutes to over an hour depending on how busy they are.
No interview. They aren't usually IOs. Some may like to talk and ask questions, but it's not something officially on your record.
There's likely not "thousands" of people at an ASC in a whole day. Maybe a few hundred tops?
 
As for a typical timeline at Indianapolis, I would have to defer to others. We did ours in Philadelphia - one of the busiest (but certainly not the busiest) in the country, and our time just had a handful of others there at the same time. There was only seating for maybe 100 people total.
 
Good luck.

Medical examination info; https://www.uscis.gov/policymanual/HTML/PolicyManual-Volume8-PartB-Chapter4.html:
 

USCIS Q and A that states its free to file I-765 and I-131 in your case; https://www.uscis.gov/news/questions-and-answers/uscis-issue-employment-authorization-and-advance-parole-card-adjustment-status-applicants-questions-and-answers:
 

Since you are about to file for AOS you are eligible to concurrently submit a FREE I-765 for an AOS-based EAD. It's optional, but highly recommended. The category of this EAD is (c)(9): https://www.uscis.gov/working-united-states/information-employers-employees/employer-information/employment-authorization Select "Initial application" on the I-765.
The I-131 is a multi-use form, so for your case you don't need to answer certain parts: https://www.visajourney.com/forums/topic/680103-i-132-advance-parole-question/ Or you can do something like this:
It's optional to file, but highly recommended; and if a I-765 is concurrently filed then you'll receive a combo card:

You are eligible to concurrently submit a FREE I-131 for AOS-based AP.
No need to do it now; it can wait. You'll need it for the interview. At the AOS interview, the medical shouldn't be older than 60 days*.
*The actual rule is that USCIS should receive the medical within 60 days of the medical exam being performed. So you can submit it now, but it is recommended to submit it at the interview.
If you don't maintain your F-1 status then you'll still have authorized stay allowed by the US Attorney General because of the pending AOS; the I-485 receipt notice or the AOS EAD is the proof of this. Also, more reason to include the free I-131 for AOS-based AP.