Basement Bathroom Remodel Venting questions

[Yazen]

Hey all,


First time posting from Lynchburg, VA. Did quite a bit of reading on IPC codes and what my options are for doing a basement bathroom remodel from a half bath to a 3/4 bath. I have added a lot of pictures because the current rough in piping doesn't seem to make sense to me...I can hear my Lav gurgling and noticed that the lav wasn't vented except maybe at the connection to the sanitary underground...

The attached drawing is my proposed drawing for the bathroom. Sorry for the poor quality drawing...

I wasn't sure if I could tie in my new dry vents into the existing dry vent in the ceiling. The existing one is 1.5" which i wish was 2" but thats what I have...I was wondering if doing that would be acceptable. It doesn't appear to be a drain for anything unless i am interpreting it wrong... Hopefully I can get some guidance.

Proposed basement bathroom setup https://imgur.com/gallery/5JLnrvQ
https://i.imgur.com/7cHAkWz.jpg
https://i.imgur.com/2g9RAt2.jpg
https://i.imgur.com/LHdrkmO.jpg
https://i.imgur.com/OdCGhXw.jpg