In regards to the questions (Ive only completed first year actuarial studies so I may be wrong on some points)
1) No interview required unless you are going for co-op program
2) I have plenty of friends with uai lower than 95 doing fine in actuarial studies (getting Ds, Cs, HDs - mind you they had pretty good marks in 4u and 3u maths). UAI indicates nothing in terms of difficulty of course and propensity to suceed in actuarial studies (As uai is heavily determined by english, which drags the uai down for ppl like me). Engineering is a lot more difficult than commerce in terms of workload (engo 20+ hours vs commerce ~12-14) and content (epic fail rate for first year mechanics- heard from a friend doing engineering)
3) Recommended total of 3u and 4u is around 180 - so rajeenth i reckon you should be able to cope with first year maths at least. Also, a lot of the stuff in Maths for Actuarial Studies (MATH1151/1251) is revision of 4u maths (integration, complex numbers). If you only did 3u, I would recommend at least E4 (highest band??) cos some of the stuff in maths can get pretty hectic.
The most important thing about doing actuarial studies is not the degree itself, its actually getting exemptions from Institute of Actuaries Australia. That mainly involves getting 70+ in all actuarial courses, which is rather diffucult. fortunately one does not have to excel to do so, and there are plenty of ways to get help in UNSW (an awesome institution
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
) such as Peer Support classes, where higher year students go over the stuff learnt in lectures and make sure you understand it.
Good luck in your uni applications