Congratulations! It's exciting to establish your own rules of engagement for your role, although I'm also guessing it seems a little overwhelming at the same time!
1. If you are focusing on compliance, review and general monitoring 20 hours should be enough, although having a clause that there may be additional hours due to unforeseen circumstances (think Worksafe visit or notifiable incident) could blow that at. Also, remember to schedule in your own professional development and training. If you are maxed out, this will be the first thing to go.
2. Reporting to the CFO can be good and bad, on the one hand, you are talking directly who signs off on money stuff, so you can start canvassing early for next year's budget. On the other hand, the CFO may have limited bandwidth for HSE issues (Or simply be MIA) during a budget review or end of year process). You need to be quite strategic about this.
As far as job descriptions go, take a look at INSHPO's 'A Global Framework for Practice' https://www.inshpo.org/work
look at pg. 16, there is a useful table of skills and competencies that you can put into your JD
3. As far as trying to start up full-blown HSE committees while you are still new to your job, I'd recommend starting small and establishing your 'friendly' stakeholder group first.
a) Establish HSR's for each site
b) Get the Operation/ Site Manager on board (do a proper project plan that explains who will be involved, how they will be trained and the time commitment).
c) set up a communications plan to roll out the plan to workers who might be interested
d) hold elections.....
You may find the following useful:
UK govt Guide 'How to set up your H & S Committee' NB this does not use the same words as our legislation, however, it has some excellent ideas on 'How To...' http://www.hse.gov.uk/involvement/howtosetup.htm