Even using the e-cig flavour concentrates, DIY juice only costs £1 per 10ml at most. I went straight into DIY as soon as I got my first ego/CE4 kit. It's not only cost, but also the flexibility that I love. I found the 80/20 70/30 PG/VG mixes too harsh and experimented until I settled on a 50/50 blend.
As far as the smoking goes - I would say just do what you feel like. I went from 17-20 cigs per day to 4 per day without trying. The vaping just tends to stop you thinking about having a smoke most of the time. Many people just stop wanting to smoke from the first day.
I'm still smoking those few, and I'd like to let them go. I know I don't need them anymore- it's just psychological.