Can you do literally everything in one day? I don't know, honestly think you can do anything you desire to do if you're all by yourself in one day, especially if you arrive before opening (even if you do not get early park admission at Universal, from my experience they'll let you in 15-10 minutes early).
During the time you're going it shouldn't be too crowded, so if you go early you should be able to cover a lot of ground. From experience, I recently decided to go for a "half day" (I'm about to do it again tomorrow, woo!) which ended up being 4 hours. I rode Transformers twice, the Mummy once, Men in Black twice, Hogwarts express twice, Forbidden Journey, The Simpsons, and watched Horror Make Up Show and Terminator 2, which those two are about a half hour each. Oh, and I also managed to sit down and have a meal. That was between 9-1pm, which technically is less time than that cause by the time I got to my car it was exactly 1 and it takes time to walk back to the car.
So, can you literally do everything? Don't know. But I'm sure if you put your mind to it, plan on knowing what you want, and come early, you can ride just about anything you desire. Also, an extra bonus for going alone is single riders, which are shorter lines. For IoA singer rider attractions are Forbidden Journey, Spiderman and the Hulk (which will be open by the time you go). For Universal, it is Men in Black, The Mummy, Transformers, Rip It Rocket, and Harry Potter and the Escape from Gringotts.