WordPress website for custom use?

Hello everyone, im thinking of setting up a business similar to “just eat”. This will require other takeaway shops to be able to become partners through the website or mobile app which will both work in unison, this will then allow customers to order what they want from their favorite restaurants. Now this is where the real question comes in. To save money im planning on using a template from WordPress, therefore i wont have to pay a web designer to make a custom website design from scratch (for now at least) but i was wondering if it would be possible to have such complex algorithms on a website using WordPress which will work together with a mobile app, like being able to use Facebook on a PC and on mobile, or would i have to go with everything being completely custom made?

i hope that all made sense and would greatly appreciate it if something could help me out as im still very knew to all of this. Thank you.