Sounds like things are a lot stricter than when I had my dd 3.5 years ago.
Just remember these are guidelines not the law and they have to be "over the top" because the are written for those considered the least hygienic (SIL is a GP and has been on many WHO seminars about infant feeding, also has two of her own).
The water being 70 degrees when the powder is added is nothing to do with sterilising the powder. It's a dry substance with no moisture in it, therefore bacteria cannot breed in it. They say 70 to sterilise the bottle in case it hasn't been done adequately before the feed is made.
As long as you know your hygiene is good before make a bottle up (washing down surfaces and the sink with anti bac stuff and washing your hands, thorough sterilising the bottles etc) there is no reason why a bottle of formula should be a problem.
If I was going out for the day (I'd do this everyday anyway tbh).
The night before I'd add the boiled water to all of the bottles and put the kids on.
I'd then use a powder dispenser pot and measure out all the formula powder I'd need for the bottles (I used two or three of them before solids). That way of I lost count it would mess up a bottle I could just start again.
I used to take out with me a tommy tippee flask that I could warm them up in and the water stayed hot for hours.
Of course each to their own, but I certainly wasn't going to make life tricky for myself unnecessarily. I did follow the guidelines to the letter when I first started ff and found it rather stressful until SIL came over one day and showed me what she used to do. It was a doddle after!