justbeing - you measure the hot water as you put it in the bottle, mix the powder into it, then you measure the second lot of water before adding it OR you know where the bottle ends up when it's made the other way and top it up to that. Slightly less accurate but 5ml here or there isn't going to hurt anyone :)
You aren't adding water to powder you are adding powder to water - then when it's mixed up you are adding more water. There are two main reasons for not adding water to powder - one is that it clumps more if you do it that way and secondly because they think people wouldn't add the right amount of water (ie they'd fill it up to 150ml rather than putting in 150ml of water).
The bottle of water - it can be a spare baby bottle, which you'd just sterilise the same as any other bottle. Sterilising is a whole other thread :)
However, in short, if a bottle is washed and rinsed properly you don't need to sterilise it, washing in a dishwasher is OK as well. The main thing is to make sure all of the milk has been washed off. Sterilising is really a safety step for people who can't/wont take enough care when washing bottles - it's a 'feel good' factor.
Honestly, relax my love. Babies are pretty hardy and it's actually quite difficult to break one x Just keep asking what you need to know and keep muddling along like everyone else.
I don't think you are trying to take short cuts to just make your life easier - you are trying to cut down the 'wait' time for your DS. However, if you hang around here long enough, we'll be able to convince you that you can indeed make shortcuts to make your life easier and still be a great Mum!!
I don't know why the bacteria in formula issue isn't better known - I guess it's because if the pro breastfeeding people say it they get accused of being anti formula, the formula companies aren't going to do more than they legally have to (small print at best) and other people just forget it's something other people don't know or you hate to feel like you are criticising... if I see people make up a bottle with cold water I tend to assume they know that it's not a good idea but have chosen to take the risk therefore I don't say anything, because although it wouldn't be, I would worry they would take it as a criticism of their parenting.... it's tricky.
HV & MW's are very variable in their quality and some spout utter shit. If you are unsure about anything - ask the collective wisdom of MN :)