I think a couple of bottle should be enough - they will serve you in an emergency and you can get more if you need them. I had 2 bottles and I was glad I did because when DD was about 5 days old, one nipple was so badly cracked I was feeding solely off the other side and in the middle of the night, I felt like that side was empty - DD was screaming and I couldn't feed her. so DH rushed out for a tin of formula from the servo (next time, I will have some formula sachets on hand JIC) and the next day he went out and got me a pump - the Avent Isis one. I used my pump a LOT for the first 3 months until my nipples healed but once they were all better, I never used it again.
So point of my rambling... you mightn't need a pump at ALL. If you aren't planning on stocking the freezer with EBM you won't use it that much. I think it is one of those things you should buy when and if you need it - they are pretty widely available so you could send DH or someone down the chemist to get one. Maybe do some research and decide which one you want so if you want one later, you can get someone else to get it for you? If I had my time again, I would get the Avent IQ (it is the same as ISis but with a motor) but I never looked into them beforehand because I didn't think I would need it.