1. Your bathroom and kitchen sinks need dry vents.
2. To use wet venting for a bathroom, the kitchen waste must join downstream of the bathroom waste.
3. For a specific list of questions, I suggest typing those into a post rather than being part of the image; that way they can be copied and pasted etc.
4. You can go from 2 inch to 4 inch.
5. My list of comments are only for aspects.