I'm a full stack software developer. I build custom business web applications.
In reading your project description. I have experience in all of the things that you require.
1. I haven't done a Xero API integration, but I've done accounting applications with Quickbook API, I've implemented over 20 other API for various projects. o I will be able to do you Xero integration.
2. I don't know if you are aware but for the SMS portion of your application you'll need a third party integration as well. I've done SMS integrations using APIs from both of the two leaders in SMS application integrations: Plivo and Twilio
3 & 4. I've built mobile apps that integrate into web application that I've built. However, I would recommend against using a native app over using a responsive site. This will keep costs and maintenance lower for you, and my bid does not include writing mobile apps.
5. I've built complex routing applications using the Google Maps API, and I can implement it for you as well.
6. My web applications are customizable with both roles and permissions to restrict what your users can and can't do.
In addition, I've built deliver scheduling applications before as well.
As these are private business applications, I can't share public links, but I can provide temporary link to my development environment upon request while we are chatting.
I'd love to talk with you about your project, and show you what I can do for you..