I'm pregnant with ds2 and also have a 22 month old who is v active and demanding, as I think most of them are! 
I plan to breastfeed but looking realistically at the situation I know I will struggle at times and giving a bottle of expressed milk would be far more practical.
I'm lucky in that both sets of grandparents live close by and with ds1 were very hands on and keen to take him out and about visiting etc to give me a break and also that DH is v willing to help out with feeds which I think I will be thankful for with an energetic ds1 to entertain all day on top of the new baby. No lazy days in bed for me this time around!
We also have my best friend's wedding to attend involving an overnight stay four weeks after ds2 is due (might be a bit ambitious, will see how we feel!) but obviously if we do decide to go, ds would have to be able to take a bottle in order for me to leave his side for any amount of time.
I know i probably wont have as much time to sit and breastfeed on demand as I did last time and as DH and I only have one car between us at the moment I will also be walking quite long distances sometimes with both dc in the pram when it might not be practical to whip a boob out if needed and a bottle would be far easier to manage.
For this reason I am very interested in expressing but didn't do much of it last time although I do have a pump etc and have lots of questions.
I'm not sure how soon I can start to express, how best to establish some kind of rhythm and manage demand; basically I am a complete novice so any tips or advice would be greatly appreciated! Would I be better off offering a bottle of breastmilk as soon as my milk comes in so he gets used to it right from the start? It doesn't bother me if I don't get to actually breastfeed, as long as ds is getting the goodness of breastmilk.