Traveling to Italy for my first time ever for my sister's wedding in Florence. I am going the first week in April. Would love advice on your top "must see" cities, what the weather is like early April, if you would stay in a hotel or villa...

My first reactions to your post:
1. You haven't told us very much about yourself--your age, your interests, you sex, etc., etc., etc.
2. How about doing a little research on your own first? You ask about the "must see" cities. Duh....Have you heard about Rome and Venice? (You do mention Florence.)

The weather is springlike. See weatherbase.com or worldclimate.com for more details.

I would stay in a villa.

How many top "must see" cities?

Best wishes,

Rex

How many weeks do you have in Italy?
It will take about 6 to make a good dent.

I don't believe you need multiple weeks to see italy to truely experience italy maybe but to see it no way. Not all of us get to europe every year or two so here is my advice. I am not a expert travelor but have been to italy three times. One visit 4 days, one visit 2 weeks, and one visit week.
If your limited for time this is my advice for one week.

3 days Rome
2 days Florence
2 days Cinque Terra

People will disagree but you can get a taste.

Jaws are dropping from Greenland to Tierra del Fuego over the omission of Venice.

Oh my, yes...Venice in April.

If we assume you only have a week and you must be in Florence for the wedding, then fly into/out of Florence and Venice. Rome deserves more than you can give it this trip.