WR
My understanding of AIAA is the same as yours. You can transit non radio, if you wish, but staying above 2,000ft is recommended.
As for Stansted transits, it really depends on the workload they have at the time. You can always go under the class D between Luton and Stansted. Just follow the A10, observing the drop to 1500ft at Stansted's SW end. From there you will see Hanningfield and are nearly at Southend.
South of Stansted can get quite busy, so call Southend up early and get a service. If they aren't snowed under, they will help with possible conflicts.
Hope the weather is good for your trip.