There's a guy in my UMEP group whose doing a full 5. But it isn't just *any* 5 subjects, it so happens to include 4 of the hardest subjects ever (subjectively speaking)
Specialist, English, Physics, Chemistry, Methods +UMEP BIO
I have no idea how he manages tbh- but he shows that it's possible. I certainly think a full load of 5 is possible + UMEP, however, I think that it would be adding more stress upon yourself, whereas say, doing 4+UMEP might ease the stress significantly
options are simple: A) study hard with 4 subjects and prioritize+ focus. You give yourself breathing space and resting time but you severely limit your options as to what can go into your bottom 2 (I only have, at the end of the day, 5 vce +UMEP- bit silly of me, but then I think to myself about what other subject I could have possibly done, and I realised I didn't really have much of a choice anyways)
or B) choose 5 subjects, add quite a significant amount of stress upon yourself- but by the same token you keep your options open as to what is planned upon as being the top 4. Only do 5 subjects if your the type of person who, once commited, continues on with their heads held high no matter what. If you do 5 subjects +UMEP, and find that its an incredibly stressful challenge, but you keep your head held high and push through, then I say go for it. If you don't want to play your chances, as in, you don't know if whether you'll be able to do that or not, then I say just do 4 subjects.
By the way, despite my friend having a full schedule, he still has time to read comic books.
Also, to place things in perspective, I think there are some grammar schools that require you to do 6 subjects at year 12 (in the same year)- so that's the equivalent of 5+UMEP. It's not impossible- but it's certainly moreover a question of stress and its extent