Day 13 - train to Bellagio
Day 14 - Bellagio
Day 15 - Bellagio
Day 16 - Bellagio
Day 17 - train to Maggiore

The train to Bellagio involves actually take a train from Milan to Varenna-Esino sp?) and then walking the short distance down to the boat dock and taking a boat to nearby Bellagio.

But there are other routes as well - take a train from Milan to Como - Nord station in Como right by boat docks to catch boats to Bellagio or quicker and cheaper I think from there to Bellagio by bus.

For Lake Maggiore from Bellagio boat to either Varenna or Como to catch trains to Milan and then a straight shot north to Stresa, raialhead for tourist Lake Stresa a k a Lake Maggiore) - I found Stresa to be a neat town on the lake - a tourist town but really sweet - the famous three Borromean Islands lie just off shorte.

Personally I would fine 4 days on each lake a bit much but if day tripping to places like Orta I guess OK.

Stresa to Interlaken is straight forward by train - train to Spiez often now have to change at Brig - to Spiez via new Lotschberg Tunnel - consider a 4-consectuive day Swiss Pass as it can be very useful in the Interlaken area - use it to go to Zurich the night before your flight - I always say be in your flight departure city the night before - you never know when a railway blockage, strike, etc pops up and if you have a non-refundable air ticket...