I really want to build a bar...

[crokett™]

 b) add a PVC snap tee to the existing DWV stack, c) angle it properly (this is the only part that might be tricky since I don't see angled snap tees or sweep snap tees), 

I haven't seen a picture of your setup so this advice is worth what you paid for it, but they make Fernco (rubber) fittings that have angled tees.  From experience those are much easier to install on an existing line than hard plastic.  I used to be skeptical until I was watching an episode of TOH several years ago and they were connecting a new sewer line from the project house to the city.  They used a 5 or 6" Fernco and mentioned that is what the city specifies.  I figured if it's good enough for Boston to be buried 8' down it's good enough for my basement.

[FS7]

I've used Fernco before...always liked them but had no idea this was even an option. Looks like they make a 4" tee fitting that does exactly what i need.

https://www.acehardware.com/departments/...gJWJPD_BwE