Taking photos on other device while iCloud photo library still syncing?

I am starting with a brand new 'empty' iCloud Photo Library.

I have iCloud Photo Library off on all devices and have started by switching it on in Photos 3.0 on my Mac.

My Mac is currently uploading to iCloud almost 14, 000 items at 70GIG..

I cleaned up my iPhone and have no photos on it at all at this stage and have started with a totally clean slate.

My question is, should I wait until all Mac Photos are uploaded to iCloud Photo Library before switching iCloud Photo Library on, on my iPhone, in an effort to avoid any possible sync problems? Or should I just run it on the iPhone now while mac is still uploading?

Can I start taking photos on the iPhone with iCloud Photo Library turned on, while the Mac is still uploading it's original large content? Will this cause any discrepancies?

I'm trying to keep everything 'clean' and 'safe' but turning devices on one at a time but it seems like this initial upload from the mac could take weeks..

-Frank