Blogging does not take up much time if you're good at writing and typing. If you arent very good at those 2 things, just say no thanks or take 1 blog a month. No reason to put yourself out and if you want the blogging thing for your CV once a month is just as good as twice a month in an employers' eyes.
By possible be first year student rep, I'm assuming you mean you're going to apply for it. Competition for these spots is usually rife and your chances will be slim just cause a ton of people will probably apply for it. Again the only reason to do this, in my opinion, is to boost your CV. HOWEVER, it seems like you're headed towards a career in social care of some sort and the employment history/reference from the women's shelter job would look much better on job applications. Not to mention you will have icome.
I've just graduated with a 2:1 degree in marine biology. I didn't do an awful lot of work at the weekends , not unless it was close to exams or I had coursework due in that i'd left a bit late. Which proves it's suggests not a ******* if you're busy at weekends as long as you manage your time well. Stay on top of your course work and time will simply not be an issue. It's easy to be lazy and wait to do it later when you've got like 4 weeks to hand in a piece of work, my genuine advice as someone who's always left it late is just freakin do it cause it was doing coursework late that probably cost me a 1st in the end.
Summary:
- Continue doing the volunteer with abuse victims (good on ya btw)
- Blog once a month, not twice.
- Take the job instead of the rep position.