Hiya hun! I keep sneaking into 2nd tri. Feels weird being in 1st tri after you've had the 12wk scan, so apologies for nosing in your thread, I just thought I would put my two pence in!...
My SIL preferred to express with both her boys - she pumped for about 6 weeks for her first son. I think she did a bit less with her second, due to having her toddler to look after as well, but she had a really good milk supply and managed to pump a good stash for the freezer.
You could ask the hospital or a local baby cafe about loaning you a pump as well - you could see which one you get on with then, as they're quite expensive. I had a manual Avent one and found it really good. It was a knack getting the hang of it tho, so don't despair if you don't seem to get anything out initially - when I first pumped, I was lucky to get 1oz! - but once I got the hang of it, I could get as much as 7oz per time. Or you might be lucky straight off like my SIL, she always had great supply and got loads from day dot!
Don't know if anyone has mentioned it yet, but there used to be an exclusive pumping sticky thread in the breastfeeding section - that might have some helpful tips for you. Some of the ladies on that thread did say they found it's a real full time thing exclusively expressing, but I think if you're planning to formula feed as well, this takes a bit of pressure off you - just bear in mind, the less you pump, your milk may start to dry up sooner. They may have all sorts of other tips as well, like how to stimulate the let down. This can be a struggle sometimes, you can sit pumping and nothing comes out, then you start stressing more and it's a vicious circle! I randomly found holding the pump at an odd angle just initially encouraged the milk to let down - others say stroking the end of the breast or having a picture of your baby close also help to start it flowing.
Sorry I am rambling on! - I used to volunteer for the Baby Cafe when our son was born so love chatting away about feeding and expressing!!! Good luck with whatever you decide hun x