Re percentage of juice u have to add to the juice depends from manufacturer but it's very common that u may need to add less or more than the recommended..
Many of us start lower than the manufacturer....and then we did see what we like...
Many times different flavors from same brands may be stronger and u won't like them even at lowest recommended...
This all means it takes time to settle to some juices how u want them and bad part is the steeping cause takes time...
U can follow recipes and start with a kinda simple one..
Myself I don't follow recipies...
About steeping I have heard a lot and read online but anyways..
In my opinion this is like that..
There are some machines that help steep juice that heats it and steer it...very expensive and overkill in my opinion
Some use other devices like ultrasonic and such..
I have tried the warm baths and shakes....but it can ruin the nicotine if u do veeery hot baths and if u do it right yes it can help but still need days...
I actually usually see that after one week is the least steeping I would do........and after 2 weeks is usually when i vape them cause it gets even better....
And some flavours change may change even more after 1month..like it takes long...
It's nice when u make some juice already steeped and then u buy before those end so that the next batch u make will be steeped until u vape it...
So long story shorts u can't judge a juice when hasnt steeped for one week..
That's all from my experience but I am not any old vaper veteran.
I just let it sit in a dark place....I may do a bath at first and shake it and then I just let it sit and shake it a bit every night or something....