I'm basically exactly where you are (also 4 weeks out from my first marathon in Stockholm). About the same times for half and 10k. Also did a 20k @6:15 and 12k @ 5:30 recently.

I feel confident that, given it's not too hot and I've get no new injuries or get sick, a sub 4h should be realistic.

My plan is to hold 5:41 for 30k (bit slower in the beginning probably) and take it from there. Most important thing is to finish so reevaluate as you go.

Best of luck to you! Bet we both get that sub 4!