Wow... Colleen... you brave woman...4 lo's...Yikers!
Well, I'm no expert, but we did have some issues with BF'ing in the beginning so I had alot of help from the team of LC's in my community health dept. So I'll share what they told me.
Pumping can definitely improve your milk supply, but mostly, suckling increases milk supply so keep that in mind as well. I still pump to this day and it's mostly to have some independence and to be sure she's still interested in her sippy cup as well.
How- this depends on whether your baby will be feeding on both sides or not. You may pump both sides or just the one they don't feed from that time.
When-you can pump right after a feed to ensure the breast is emptied, especially helpful in the beginning when they are just learning to breastfeed. When my lo started sleeping through the night early I would pump in the middle of the night to increase milk supply.
How often- that depends on your purpose for pumping at various stages. If you want to pump to increase supply in the beginning, pump after every feed. If you want to pump just to store milk for bottles, then it depends on how much you get from one pumping session, as you may only need to do it once. The LC's said that if I'm pumping for storage, to pump after the first morning feed when you have the most amount of milk, your body will adjust to the supply. So if you are feeding on one side, you can pump the other right after you breast feed the baby in the morning...or if you are feeding from both sides, you can pump both sides an hour after you breast feed first in the morning.
Nipple-I used Playtex Natural Latch and Advent. You purchases sound good though. You do want something that most resembles the breast, especially in the beginning, but you may have to try different ones. I like the one with the multiple holes...cool! R u in the UK? Nothing like that in Canada...
Bags-You can buy special storage bags..didn't have money for that, so I bot bottle liner bags and frozen in those then put them in a ziplock and into another ziplock..never had any freezer burn at all
Milk on hand-I usually have milk for a week on hand as I pump, but I only give one feeding a day, if that with a bottle, and I also freeze it in cubes for cereal.
A lot of these questions about how often and when is going to depend on the baby and how well she/he does at the breast. I was so ready to give up bf'ing actually...But the LC's convinced me to stick with it...I just wanted to pump and give her the milk..but they said, no...wait...relax...she's not in any trouble, lets figure this out...so we did that...and all is great! All was great at 2 months. So it took a while for me to relax about everything...and I AM a first time mom..

Hope I was able to help a little. Good luck with your full house

Leanne