I _DO NOT BID_. As I remember your org project, I am not wondering, that you re-post it. As the functionality, you request, can be done, but _NOT_ on the MR3020, because of lack of resources.
Relevant Skills and Experience
Look at my feedbacks, and you will recognize sevarl projects regarding captive portal/hotspot/Wifi, on openwrt/LEDE.
Choose a better suited device (similar price), and you can get what you want.
Proposed Milestones
£111 GBP - no delivery
Additional Services Offered
£1 GBP - Recommend suitable device , similar price, more resources.