1) It doesnt matter as the boost applies the same amount regardless of level. I feel its best to do it early as possible so you can enjoy those extra stats a little longer.

2) Theres some big math equasion behind it, can't remember the post or formula though, I'll let someone else who knows better answer this one.

3) It's all about luck, and perhaps how fast you can flip through the reset stats. Some days I get really lucky and get a few +12 sailors after like 10 minutes of rolling, then some days I get only 1 +12 aircraft crap after 2 hours.

Hope this helped.

I can answer all but #2 on your list... 

1) Boosting sailors (Premium Sailor) does not matter when you do it since it is always going to be      he same 20% buff added to the ability.

3) Rolling single ability +12's is a long slow process. Getting 2-4 in 2-3 hours is pretty decent. I know myself as well as some other unfortunates RARELY get one. As for the secondary stats on the +12's you have to remember you are playing a numbers game. You are trying to get a rare sailor just on the +12 but getting a useful secondary stat that's any good greatly lowers the odds of getting one.  

On the 3rd question I probably should've added that those were on good days (once in a blue moon)

On the first you guys say that it doesn't matter but I was thinking that as it does 20% of growth wouldn't be better to do it later after classing since 20% of a +25 current growth is better than 20% of +12 original growth, but again I was not certain if this is how it worked and that is why I asked.