Hi Jenna,
There is alot of different advice about expressing and different people have different opinions. It is probably best that breastfeeding is properly established before beginning to express and offer your dd a bottle. I found that we were ready around 6 weeks. Skipping feeds so early on can really affect your supply...giving a bottle when you should be feeding sends a message to your breasts that milk is not needed. It can also lead to engorgement - if your baby is not nursing, but is instead feeding from a bottle, your breasts may become engorged and this can lead to mastitis - this may be what your midwife is referring to. However, you will not necessarily get mastisis.
Some women chose to express and offer a bottle very early on and do so successfully. Others find that it really affects breastfeeding. Even if it is your own expressed breast milk in the bottle, one bottle a day can lead to a baby starting to feed less well at the breast and the increasing ?need? to give more bottles...one bottle can lead to two, then three etc etc.
Re: nipple confusion, there is again alot of different opinions about this. Personally I found that when I gave my DD a bottle she did seem fussier at the breast afterwards because the flow from the bottle was so much faster.
I am saying all this but I totally understand the exhaustion you are experiencing at the moment. It can feel sooo overwhelming...my biggest peice of advice would be to sleep when your DD does. Seriously, make the most of the time in between feeds to eat, sleep and rest. It really will get easer over time - before you know it you'll have a bit more time in between feeds. What you are feeling is normal - I was so shocked by how much my DD fed and how often!
When you do decide to express, as far as I am aware, it is recommended that you express immediatly after your baby has fed. Hand expression, if done properly, is gentler on your breasts, but I found using a pump faster. In the early days, you will need to express when your baby would normally be feeding (i.e when they are getting the bottle) to maintain your supply and prevent engorgement. This gets easier over time though.
Likeacandle, it is not recommended that you frequently use frozen breastmilk for feeds - if you have frozen it, chances are it is weeks old and the composition of the milk may not be the same as your current composition. Someone will correct me if I am wrong about this.
Re: dads playing a role - feeding is one of the many elements of parenting. Dads can get involved in so many other ways. I'd really discourage against expressing and offering a bottle fot his reason alone.