There are lots of books out there that cover it -- including Beyond Disney: The Unofficial Guide to Universal Orlando Sea World, and The Best of Central Florida, and Independent Guide to Universal Orlando 2015...
There is far too much to cover in a simple posting here --- you can also do a search through the universal forums in here...
IN general you CAN do both parks in one day. Their own website is a good place to start. The hours very as much as they do at WDW so you have to check their website for hours of opening from day to day.
There is plenty to do for all ages -- but the parks are built around thrills. The shows pale in comparison to WDW's , and even doing both parks you will probably run out of things to do by late afternoon, especially if you don't do all the coasters and you get started at park opening. As a general point of reference, Universal Studios is built around entertainment (think DHS on steroids), while Islands of adventure is built around thrill rides.
I go about every 8 or 9 years just to see what is new. Frankly, one visit a decade at Universal is enough for me. I spent most of my time this past winter's visit doing the Harry Potter stuff - starting at Diagon Alley in US and then taking the train over to IOA to do the Potter stuff there...