Hi Gokul22!
I don't know enough to answer all parts of your question, but I'll try answer the parts I can.
-At Monash university, the "ideal" pathway to becoming a psychologist is through 'bachelor of psychology', however, it is possible to do an accredited major in psychology through B. arts or B. science for 3 years, and then get into the honours year of psych for 4th year.
pathways @monash
(https://i.imgur.com/XmFUs97.png)
-AT Monash you are able to transfer courses generally if you have a high enough WAM (70+ish), but depends on number of places available.
-UCAT is not necessary for psych