Advice on 4 week Summer Europe Trip

Hi everyone, My girlfriend and I are planning a 4 week euro-trip for this summer and I'm worried we might trying to do to much.

 

Current Plan

Frankfurt: 3 Nights

Prague: 3 Nights

Krakow: 2 Nights

Budapest: 2 Nights

Zadar: 4 Nights

Florence: 3 Nights

Cinque Terre: 2 Nights

Lauterbrunnen: 2 Nights

Paris: 3 Nights

Seville: 3 Nights

total: 29 days

 

We're going to fly into Frankfurt from the US in late June and stay there with family, then start the trip from there and use trains/buses/ride sharing to get around. We'll take a ferry from Zadar to get to Italy and catch a plane from Paris to Seville and then fly back to the US from Seville. My girlfriend has never been to Europe before, I'm originally from Germany but haven't been back in a decade.

we've already looked into the cost of travel and it seems like it will be cheaper to buy individual tickets to the destinations and use night trains/buses/ferries/ridesharing to get around rather than the eurorail pass. We just need to buy the tickets as soon as they're released. Also Ryanair seems like the way to go for flying in Europe.

 

Some questions

1. Is there anywhere on the trip you would recommend skipping and adding nights to somewhere else?

2. Does anyone have recommendations for a good backpack that can be used as a carryon? The ospreys seem nice but expensive. Would like to keep the price <$150

3. Recommendations on what to bring/pack? Cell phone? Computer?

4. Any advice to two people who have never traveled Europe alone before?

5. Things to do/see in the place listed?

 

Thanks for any help!

Edit: formatting