First, congratulations on your graduation!
I'd start with a little pruning. Choose one Italian destination (Florence over Venice) and one Eastern Europe city (Prague over Budapest).
Do Prague to Berlin via train, via Dresden (itself worth a visit).
Likewise, Paris and Amsterdam pair nicely as there are superb train connectionstation between the two (stopover in Brussels easy).
Reserve the Avios for the segments that will let you avoid spending too much of your precious time in transit.