Hi H.,
I have the Medela pump in style advance and I've been very happy with it. I haven't had a problem with finding bottles to fit the pump. I have 3 different types of bottles (Medela, Gerber, and one other one) and the pumps fit all the bottles.
I'd recommend that you find a lactation consultant, either an independent one or one through the hospital where you are delivering, before the baby is born. I wasn't latching the baby on deeply enough and I had sore, blistered nipples the day after the baby was born. The recovery nurse in the hospital gave me a nipple shield, and the lactation consultants don't like that because it limits the amount of milk the baby receives, and can create a shallow latch that just makes things worse. You really should have a resource you can use within the first few days. The lactation consultant will also help you weigh the baby the first few weeks to make sure the baby is gaining weight properly. They can also help you find the correct size nipple shields to make pumping more comfortable.
There are some women who have an awesome milk supply and others who struggle to keep up. Since you don't know yet what your experience will be, I'd recommend you do what the other ladies recommed below and build up a stash in your freezer before you go back to work. My lactation consultant had me pump for 5 minutes an hour after the baby's first morning feeding starting when she was two weeks old. Your milk supply will be highest in the morning, and if you only pump for 5 minutes there will still be enough milk if the baby wants to feed again right after you pump. You can freeze what you pump and rotate through it using the oldest milk first when you go back to work. You may want to pick up some Mother's Milk tea and some Fenugreek capsules so you have them in case you need them. Don't worry if you don't pump very much at first. The baby doesn't take very much - they start off with around 2.5 oz after a few days. When you first start pumping, you may only get an ounce or so ( or even less). This is entirely normal and your supply will increase if you breastfeed as much as possible and keep up the pumping. I started off only getting a quarter of an ounce; the most I ever pumped was when my daughter unexpectedly slept through the night at 5 months old and I pumped and got 11 oz. If you're going to try to breastfeed for the entire first year, you will see that your supply will go down around 7-9 months, so it's really good if you have that emergency stash.
As far as how often to pump, you should try to pump at least every 3 hours. I pumped at 9, 12 and 3. The more often you are able to pump, the better your supply will be.