I will be dropping my Science component. There aren't any majors (or should I say the courses in each major) which interest me, or that there are some subjects which I'd rather not do. So an important thing is to look through the subjects in each and major and think whether you'd actually be interested in it. I can't really provide a recommendation, however, you should apply for Engineering/Science so you do have that option later on to drop one of them if you aren't interested anymore. There are other factors such as the return on an extra year of study, the cost, your overall interests etc.
There is no extra work involved, except it being extended for an extra year. Typically, you would complete 24UOC (units of credit) each semester (or typically 4 subjects, except maths has some 3UOC subjects so you may be doing 5 subjects in a semester!). Don't think a double degree means double the work load or harder work than a single - it's exactly the same workload (in terms of how many subjects/UOC), just more years.
BTW, your google searches should include "unsw handbook" since that's pretty much where the info is.
