Hi Chris
This sounds like something similar to what Polyvore do, so you may find some guidance on their website in regards to the terms & conditions and disclaimers they make.
Obtaining permission from each label would probably be the ideal thing to do, though practically may not be possible so you need to ensure you safeguard yourself as much as possible.
It will be important for you to ensure your website does not represent in any way that you are selling the items yourself or that you have any affiliation with the brands displayed on your site as this could raise issues in terms of a common law action of 'passing off'. There may also be some implications under consumer law if customers are mislead in this way and believe they have purchased the product through your site.
I would also give some consideration to any pictures or logos you use on your website that belong to another brand (ie photos of their products, their brand name) as there may be copyright implications if you haven't sought permission to reproduce these items.
There's no quick and easy answer here, so I would recommend either
speaking with a lawyer or doing some research on other similar websites and seeing how they have safeguarded themselves.
I hope this was helpful