This is less of an answer to your how question and more of a validation/market research to the restaurant idea you have.

I went to techstars with the cofounders of Nextbite (ordermark at the time) and they did very well in consolidating orders from all the online platforms for the restaurants. I don't know if they ever took on menus, but I do know that restaurants struggle with keep up to date with all the food apps. So, seems like your idea has some market validation! Good luck.