Planning is one thing - buying park tickets is another.
As macraven said, it depends on when you're going, but Universal is currently offering a "Buy 2 days, get the 3rd day free" promotion, but it's only good through early June. After that, it's still pretty cheap to add a third or fourth day - a 4 day ticket currently costs only $20 more than a 2 day pass.
So, consider buying tickets for an extra day or two - that way, you can come back to Universal, even if you have to drive from your WDW hotel, or at least stay at Universal longer on your checkout day (which is a good reason to see Universal first - since you don't know how long you want to spend there, you have more flexibility if you hit Universal first, since you already know what to expect from WDW).
Also, the rumor is that Disney is going to raise ticket prices on Sunday, and Universal won't be far behind that, so consider getting your tickets soon.
As for the length of stay... we're also currently planning our first trip ever to UO (this summer too), and after researching everything we wanted to do and how to do it, we settled on five days, so YMMV. I think that's excessive, but in a good way! We plan on taking MANY breaks for swimming and such to get out of the heat. Lots of sites like
Undercover Tourist and Orlando Informer have good touring plans, and both sites basically recommend 3 days to see everything, assuming you're either going at a slow time or have Unlimited Express Passes (as you will if you stay at Royal Pacific, Hard Rock, or Portofino, but not Cabana Bay).
As for which hotel.. I've also asked that question several times, and for every 4 people who responded I got 7 different answers. Personally, I just looked at photos of all the resorts to pick the theme I liked (Island vs Music vs Italy vs 50s), judged the walking distance to the parks (Hard Rock is closest, then Royal Pacific, then the other two basically tie), and looked at my budget (Cabana Bay is cheapest, then usually RPR, then the other two)... so Royal Pacific was an easy answer for me!