Hi aliceinwdw!! Welcome to the Universal/Islands of Adventure forum! I'll try to answer as many questions as I can, and I'm sure some other members can answer the rest or offer their suggestions for a great Universal trip!
What are the crowds like?
We usually visit both Disney and Universal every trip. I've found that the crowd levels are similar. Universal's crowds were less than Disney's over the Labor Day weekend. However, free dining was going on at WDW, which may have decreased the number of Universal visitors.
Are there better days than others to go?
I haven't noticed any days being better than others. I would say that best thing to do is to arrive early - before the parks open. The last few times I've been to Universal, the gates opened about 30 minutes early. Universal crowds tend to arrive later so you can get a lot done in the first few hours of the day.
Where do we get our tickets?
You can buy them online at the Universal website which would save you some time by not waiting in line at the parks to buy tickets.
Are there discounted tickets for FL residents (w/FL IDs)?
Check out the Universal website for more info: Florida Resident Discount Tickets at Universal Orlando Resort Or you can check out the 7 day pass for $89.99: Orlando Discount Tickets at Universal Orlando Resort
How many days should we allot to visiting the park?
I don't know your schedule, but I would suggest at least two days to experience both parks.