I don't have a modular PSU because 6 years ago there was still quite a premium on them. However in 2016 there is no reason not to buy a modular one. You know corsair makes modular PSUs as well....
The PSU is possibly the longest lasting component in a PC so no reason to skimp on it when you are not limited by an exact budget.
And yes RX 480 8GB + FreeSync is far better value than 1070 + G-Sync provided you are not going to put the arbitrary restriction of 5 year cycle on yourself. I am sure AMD will continue to do fine for 1080p gaming in the near future.
I personally would buy a 1070 with a non G-Sync monitor but that's because I have never really been bothered by regular V-Sync solutions.
All depends. It's such a hard recommendation.
I just day get an adaptive sync monitor no matter what. I can't recommend someone to get into freesync simply because it's cheaper when I'm in the predicament I'm in where I want to 4k game but no gpu to do so with until Vega, where that never happens with Nvidia due to their buttery smooth gpu launching.
You just have to choose what method works for you. There isn't a better option.
I prefer freesync because :
I can wait for gpus through amds insane release cycles
I don't want to fuel Nvidia gsync. I want them to give up and support a standard that works for everyone. Then I'll buy Nvidia gpus more.
More options. I can't buy a monitor I care about with gsync. My monitor I'm using isn't even available from an American company. There won't be a gsync monitor to match my specs forever.
So all depends on exactly what you want.
It's just so hard to decide without the op fully understanding what we do.