I introduced a bottle for the dream feed at about 4 weeks and it's worked really well from the start. I expressed for the first 5 weeks or so as I really didn't want to give formula - so many people tell you breast is best that I ended up thinking formula was poison - but I relaxed after a while and gave DS formula feed for his DF and he hasn't turned green yet! My supply didn't go down at all from this. In fact I was waking in agony with swollen breasts and wet sheets at 5 every night! What I do now is express at around 10pm and use this in a bottle for the DF. Sometimes I top him off with extra formula if I think he's extra hungry or I don't express as much as usual.
Sometimes I think what's the point of putting the bresat milk in a bottle, but I think it's worth it as it means he's used to taking a bottle ready for going to nursery (in 3 months - I'm dreading it) and also other people can give him that feed if I want to go out / have a drink. This is working really well for us at the moment.
Regarding pumps, I tried a manual and an electric one and would definately say it's easier with an electric one, although the manual one was fine it can hurt your hand after a while! I have the Medela mini pump and have had good results with it.
Good luck with it whatever you decide. Get into a routine first though and make sure you're comfortable with the breast feeding before introducing the bottle. It can take quite a while to get the hang of it, but I'd say it's worth it.