You've got two fixtures wet vented: the toilet and the lavatory (bathroom sink). I'm not a professional plumber, but I lived in a house with an almost identical setup, and the toilet had a tendency to siphon the trap for the shower when it was flushed, especially if it had a fairly large load.
Inspectors vary as to what they'll approve, as do plumbing codes, but I think most would not okay your bathroom as drawn. In addition to the double wet vent, if you're really proposing to put the trap for the lavatory below the floor, you'd have a sink tail piece well over 24", which is a code violation. With a tailpiece that long, the weight of a sink full of water would stand a good chance of siphoning the trap.
If it were my bathroom, I'd install more venting. If you can't run vents from the lavatory and toilet up into the attic (assuming there's an attic above your second floor), then you might consider Studor vents (a/k/a air admittance valves), if they're legal in your area.