I am pretty sure it is allowed. Saw many picnics going on.

We were there 3rd wk Feb & was just starting to bloom. Hopefully you are able to see full blossom by the time you are there. Perhaps you shd check online

They had the lanterns in the garden when I went there this year in February but I don’t know if they have every year?

Parking is difficult and not necessary unless you are in a wheelchair or such. The park and castle are well served by public transport and once you are there it is great walking around the park and castle and art museum.

The time it takes to stroll around the garden will vary depending primarily on your interest in appreciating the features of the garden and the weather. I would suggest a minimum of one hour. I could easily spend four hours there on a nice day.

No assolutamente ma è bene andarci presto per godere delle sue bellezze! Buon viaggio e saluta x me i ciliegi

The Diamond Princess is the largest cruise ship that uses Kanazawa port at 115,000+ tons. Because of this I think it uses the Ohama Wharf and not the Tomizu Wharf, where the smaller cruise ships dock. Ohama is on the north side of the harbor nearer the harbor entrance where it's deeper, but also further from the bus lines. (Viking may be able to tell you if this is correct). Either way, with limited time in port (I think you depart at 3 PM), I would look into a taxi from the wharf to Kenrokuen and that museum area. It would save you time and the hassle of finding bus stops and making transfers in a place you've never been. A taxi to Kenrokuen should take about 25 minutes and cost somewhere around Y2000 (It cost me about Y1000 from the station to the garden). If you have 2 or 3 people to share the costs, the convenience and time saved would make it worth the extra yen.

Nope no bikes allowed. But you can park your bicycle outside the garden. But the town itself is walkable.

I didn't know the answer but I see someone else has replied with that. However, if you have the choice, get there early. It was very busy when we visited mid morning and hard to experience the tranquility. Have a nice time.

Yes four hours would be enough time.