New upstairs bathroom advise

I have an old 1920 home in Portland, OR in Multnomah County and I need to know two things.

1. Can I have a wet vent?
2. What size does my vent have to be?
a. If wet, minimum size of wet vent section and minimum size of dry vent section.
b. If dry only (I will have to run a separate vent and pipe) minimum size of dry vent.

It will look something like the drawing below.

Thanks
Holly

No. If you tie into the pipe as shown the 1st. floor toilet will no longer have a vent.