Disclaimer: I am not CSE, but I know quite a bit about the program for reasons I will not disclose
Will advisers help in choosing the right courses to graduate on time?
Yes they will. Dr. Kiethly, along with other course coordinators have spent a lot of time making sure that nearly any student can graduate in 4 years (even those who still have to take algebra as a first math class). Advisors will have course plans for 4 years that you can follow.
Is there much benefit to gradating in four years or am I better off spreading it out a little more to reduce stress and burnout?
That's up to you. Personally, I think 3 years is easily done, especially for one degree. Do a couple summer classes here and there, and you can easily shave off two full semesters.
Just how difficult is a computer science degree to earn at UNT?
Depends on how difficult you make it for yourself. No professors wants to fail students, but there are professors that will fail students when the students haven't a clue of what they are talking about. I wouldn't necessarily say that CSE at UNT is particularly difficult in comparison to other universities, but you shouldn't assume it is a cakewalk.
What kind of opportunities does UNT offer in the realm of internships/job searching?
IIRC, the semesterly job fair has a good amount of companies looking for CSE interns and jobs. I'm not sure if professors themselves will help you, unless you already had something in mind. I do, however, strongly suggest you join a lab and a project. If the project is properly funded, you should be able to get paid as well.
What kind of computer do you recommend for studies? I currently have a decent midrange HP Laptop[2] with an i3, dual booting Windows 8.1 and Linux Mint that I have little complaints about except display quality. Would a Macbook or similar tier laptop (XPS 13, etc.) serve me better in the long run?
That depends on what you like. I'm personally a mac person due the unix environment. Personally, I'd get at least an i5 with a decent keyboard and mouse/trackpad, but others will help you there.