I'd say 75+ in ACTL1001 to do reasonably well in later years. If you get a credit, you will still be able to manage 2nd year ACTL subjects, but you might be struggling. And I guess it depends on what you mean by 'reasonably well'.
If you gain the following grades in ACTL1001:
Pass- you should have some serious thoughts about whether you want to continue.
Credit- you should consider if you are willing to put a lot of work into further 2nd year subjects. Ask yourself if you think you were capable of doing better in ACTL1001.
Distinction- you'll be okay in 2nd yr, but again, you'll need to work hard.
High Distinction- congrats! You'll be fine, but don't slack off.
Take ACTL1001 as the benchmark for further studies. If you did your best in ACTL1001 and didn't do too well, perhaps you should considering dropping out. If you are not prepared to work harder over the next few years, maybe actuarial isn't for you.
ACTL1001 filters out those who don't want to work hard, and those who simply aren't capable of handling the actuarial courses. Yes, ACTL1001 is hard, but it stops people from wasting their own time in future years, as well as for Sachi to have a little bit of fun torturing us.
But hey, exams haven't even come - so for now, study hard.