I am about to get temporarily married to a woman who I later planned on getting permanently married to inshallah. I heard somewhere islamically I am allowed to see her without her hijab on so I know what hair looks like because of the sincerity of my intention. Can I do this? Is she allowed to send me pictures? What is the limit to how much of the woman I can see before the Mut’ah takes places

You are allowed to see her without Hijab and also the size of her body (if she is wearing tight clothes) if this will make a difference in your decision to marry her. So yes you can see her hair, neck, arms and so on. But if you are already set on marrying her, then just see her after you do the Mut’ah contract.