(I still want to go to Italy, with sicily toping my list
Malta’s ok, nothing special, but transport around the island’s pretty good. There’s a fast ferry from Valetta-Pozzollo with a connecting bus to Catania so a day or two to Malta from Sicily is very do-able if you’re based on Sicily’s east coast (Taormina, Catania, Syracuse). directferries.com will give you times/prices
Blue lagoon boat trips, good but busy during tourist season. we went with English Rose or something similar cruises from Mellieha and they provided snorkeling kit – the crystal lagoon is definitely worth a swim around in..
I’d say 2 days would cover Malta and Gozo.
Mosta Dome is worth a few minutes, and the town of Mdina just for a wander if you have the time to spare. the streets are all on curves so you cannot see further than the flight of an arrow. Apparently.