Newborn babies feed constantly - if they're not sleeping they're feeding/suckling. This is entirely normal and how things are supposed to be, so do be prepared to shut up anyone who tells you they "only need feeding every four hours". It does tend to be worse in the evenings. Night time feeds are important - this is when the "make breastmilk" chemical is at its strongest.
Breastfeeding can be hard work initially, so the most supportive thing your partner can do is ensure that you only have one job as a new mum, and that is to feed your baby. So get him (and relatives) to help with all the housework, bathing baby, changing shitty nappies and feeding you - lots. You will never have known hunger like it! You will need this support for at least the first 6 weeks. Also find a local breastfeeding support group - there is nothing like the support of other mums going through the same up and down emotions.
Expressing does take time - I did it in the early days because my nipples were raw with bad latch and internal thrush. I expressed in the afternoons so that DH could do a feed when he got in from work. There were days when I expressed every feed to get through the pain, it can be done but it is hard work.
Expressed milk will keep in the back of the fridge for up to a week, and in the freezer for 6 months for an upright, 12 months for a chest freezer. Freshly expressed milk will be okay out of the fridge for between 4-6 hours depending on the ambient temperature. If you're planning on going back to work then use the excess supply of the early days, when your body is working out how much milk to make, to build up a freezer store.
There is no need to sterilise if feeding breastmilk - just use very hot soapy water and rinse well.
A newborn babies tummy is the size of a marble, and at a week old is the size of a walnut. Use common sense when deciding how much to feed. I think DD was taking about 20ml per feed in the first couple of weeks, gradually increasing.
The Medela Haberman teat is great for babies who are switching between breast and bottle as it is the only teat where baby has to actively suck to get any milk out. It is sold in large Mothercare stores or online - don't be put off by the "special needs" label, it helps prevent nipple confusion.
Good luck - for many mums the first steps on the breastfeeding journey are incredibly hardwork. The pay off comes when you don't have to get up in the night to make bottles, and when baby is instantly soothed by being put to your breast.
There is also a little milk-drunk smile that bf babies have, the smile is beyond words but every bfing mum will know what I'm talking about. It's the smile that is the reward for all the early difficulties of breastfeeding.