Prednisone

All corticosteroids, both oral prednisone and IV prednisone, give you side effects. Side effects usually begin showing up after 2-3 weeks of daily usage with the oral pred with my experience. I've never been on the IV pred so I cannot say how quick it kicks in. Higher dosages of prednisone (40mgs and higher) in general often give energy bursts, insomnia, night sweats, more odds of being very emotional, and other such fun things. Those go away as your lower your dosage (likely below 20mgs in my experience).

Yes, everyone gets side effects from pred (if you are on it for at least 2-3 weeks) and, No, there's no way to prevent yourself from getting side effects from it. Everyone gets some side effects but not all of the side effects, and they seem random person-to-person. If you're starting at 30mgs then you are more likely to have increased appetite (which can lead to weight gain), acne, bloating, and other things of that nature. Hopefully, you are below the dosage that causes insomnia, as that can be rather annoying. Avoid salt best you can which can help with the bloating. Acne is hormonal (from the steroid) and very hard to treat until you are off of pred. Best you can do is cover it up with makeup.

I agree with Gonk. I would be more worried about how much the pred will help your UC condition, particularly once tapered off.