And are any of the listed events "all mod cons" i.e. lap of luxury rides?
At the high BOB-level: none.
Marche 600: no support
Alken 600 (my organisation): optional bagdrop/ basic breakfast for those staying at the Ibis hotel in Koblenz.
Oudenaarde 600: I don't know, new organisation. The route does 2 loops, so you can sleep/resupply at the start
Ostend/Middelkerke 600: No support, 2 loops
Gent 1000: I don't know, new organisation.