If you can heal heroics you can heal nax 10. It's not that hard to heal there (only patchwork would be a struggle at the start.
I would try to get
16-17k mana.
1.8k sp self buffed (EL + totem
300 mp5 while casting.
These are just rough figures tho. If you get the items on this list
http://wow.allakhazam.com/db/class.html?wclass=8;mid=1231179261143664047#m1231180575140774203
you'll have way more then the above figures. I had it when I started and I never had any problems whatsoever. And I've only started doing nax 10 once i've cleared 25. So I reckon with the above stats you'll be safe.