I can answer one of your problem:
Content difficulty doesn't matter as almost everything is based on ranking/percentile (study score, atar, sac moderation, A+ cutoffs, scaling....etc.). So if it's an "easy" subject like further in terms of content, then it is also "easy" for everyone else. Since wanting to well in further, you'll want to get in the mid 40s to alleviate the unforgiving scaling. Coupled with little mistakes that will determine who will get low 40s and who will get high 40s, cause further to be highly competitive (Not just further, they are many subjects like so.)
So go for a subject you're passionate in or you think you'll do well amongst the rest as that will be your actual advantage against your competitors, not the easier content difficulty of said subjects